Everyone has their own preferences concerning learning, but it's not easy to know what those are when learning a new subject. I found YouTube tutorials to be very valuable, but was kind of overwhelmed when I did searches that came back with hundreds of hits. Below is my current list of subscribed channels; they may be helpful in starting out.
All channels are GMS-specific unless otherwise noted. I include the date of the most recent video because that's an indicator of how active the channel is.
Beyond Us Games
"We are a small games development company with a passion for game development and helping others learn to do the same. Here you can find tutorials for common GameMaker questions, example projects, and eventually sneak peeks and previews of current games we are developing..."
Most recent tutorial or episode as of July 7, 2018:
2 weeks ago
Code Workshop
"How to make games using Game Maker Studio."
Most recent tutorial or episode as of July 7, 2018:
10 months ago
Electric Donkey
"Hi! I love to code and that's why I made this channel. I want to give all of my GameMaker knowledge away to you guys."
Most recent tutorial or episode as of July 7, 2018:
2 days ago
Extra Credits
Not GMS-specific, but generally excellent game dev topics.
"Join us on Extra Credits every Wednesday as we take a deeper look at games: how they are made, what they mean, and how we can make them better."
Most recent tutorial or episode as of July 7, 2018:
1 day ago
FriendlyCosmonaut
From her Patreon overview:
"Right now, I'm making tutorial videos for Game Maker Studio 2, a game development engine. I've covered topics including dialogue, cutscenes, object states, optimisation, and more. I'm also making a long-term tutorial series on making a Farming RPG, taking inspiration from games such as Stardew Valley, Harvest Moon, and Animal Crossing."
The videos are excellent and the creator is a woman, so if you want to encourage more tutorials from an under-represented section of the game dev community, you might consider supporting her work by contributing on her Patreon page.
Most recent tutorial or episode as of July 7, 2018:
3 weeks ago
GDC
Not GMS-specific, but generally excellent game dev topics.
"Welcome to the GDC YouTube channel, where you'll find clips and full length videos from GDC.
GDC is the world's largest professional game industry event, where programmers, artists, producers, game designers, audio professionals, business decision-makers and others involved in the development of interactive games and virtual reality gather to exchange ideas and shape the future of the industry.Take in in-depth talks, inspirational lectures and more from experts."
Most recent tutorial or episode as of July 7, 2018:
2 days ago
Gloomy Toad Studios
"Learn GameMaker Studio and Game Design from an industry employed professional and 12 year GameMaker veteran. I try to teach more advanced concepts that are not readily available elsewhere."
Most recent tutorial or episode as of July 7, 2018:
5 months ago
GM Wolf
"This channel is here to provide quality programming tutorials for both beginners and intermediates for GameMaker. The videos feature tutorials to help complete beginners into learning how to use game maker, as well as more advanced tutorials, covering all aspects of game development."
Most recent tutorial or episode as of July 7, 2018:
5 months ago
HeartBeast
"Hi! Welcome to my channel. My name is Benjamin and I make GameMaker Studio Tutorials, Godot Engine Tutorials, an pixel art tutorials. If you want to learn to make games you are in the right place!"
Most recent tutorial or episode as of July 7, 2018: 2 days ago
Leaf Blower Games
No "About Us" statement. Creator says he is switching to Unity eventually (for its 3D capabilities), but has over 20 GMS2 videos for the past year and states he will do more GMS game tutorials before moving on to Unity.
Most recent tutorial or episode as of July 7, 2018:
2 days ago
Let's Learn GameMaker: Studio
"A channel for those who wish to learn GameMaker: Studio. You'll find lessons here that cover everything from the basics of the interface all the way to advanced GML coding. This channel is not affiliated with YoYo Games."
Most recent tutorial or episode as of July 7, 2018:
11 months ago
Making Games 101
"Weekly 'follow along' instructional videos for creating fun, well developed games in GameMaker Studio (GML)."
Most recent tutorial or episode as of July 7, 2018:
2 years ago. Unclear (to me) if he is using GMS 1 or 2.
MentalArts
"GameMaker: Studio 2 tutorials and development!"
Most recent tutorial or episode as of July 7, 2018:
9 months ago
Mike Dailly
No "About Us," but seems to focus on remakes of classic retro games in GMS2.
Most recent tutorial or episode as of July 7, 2018:
2 months ago
MikeTheTech
"Thanks for watching! I look forward to meeting and interacting with all of you. Keep an eye out for more tutorials, gaming commentaries, and how-to's."
Wide variety of topics, including lots of GMS2 tutorials, plus game industry, Unity, Unreal, etc.
Most recent tutorial or episode as of July 7, 2018:
3 days ago
PixelatedPope
No "About Us" statement.
Most recent tutorial or episode as of July 7, 2018:
9 months ago
Rainy Day 3210
"Hello everyone! Wanting to know how to create your own indie games? You've come to the right place! I'll attempt to post at least one, maybe two uploads every week."
Most recent tutorial or episode as of July 7, 2018:
RealTutsGML
"I'm a game developer that demonstrates Game Maker Studio 1 & 2. If you're new to video game design I can certainly help you with new tutorials every week. I look forward to your success."
Also has Java game programming tutorials.
Most recent tutorial or episode as of July 7, 2018:
1 month ago
rm2kdev
"Indie Game Development Tutorials, Let's Plays and Indie Projects. Welcome to Rm2kdev a place where I share my knowledge, projects and gameplays for you to enjoy and learn from."
Also has equipment reviews, live streams, many GMS2 tutorials.
Most recent tutorial or episode as of July 7, 2018:
3 weeks ago.
Ron Flowers
No "About Us" statement. In addition to GMS2, includes tutorials on "box modeling," "IK rigging," etc. (making characters).
Most recent tutorial or episode as of July 7, 2018:
2 months ago
Shaun Spalding
Includes recordings of presentations and much more. If you've done the built-in tutorials of GMS2, you're familiar with Shaun's very excellent work.
"I'm Shaun. I'm a former Ubisoft game designer who creates tutorial content for GameMaker Studio 1 & 2 and game development in general.
"I also worked for YoYo Games for 2 years as their Community Manager, and now I've returned to my roots as an independent game developer."
Most recent tutorial or episode as of July 7, 2018:
3 weeks ago.
Stefan Randa
"I'm a multimedia designer with a BA in Digital concept development.
I love games, design and I make tutorials about these things from time to time, have a look!"
Most recent tutorial or episode as of July 7, 2018:
4 months ago
Talent Lost
GameMaker Tutorials
"I have a passion for teaching and making games, if you're new to game development then you've likely come to the right place. Here we cover many topics of Gamemaker and also we regularly check out how to implement game mechanics.
If you are just starting out with GameMaker then feel free to take a peak at my Let's GameMaker series. It's designed to get you going with the basics while creating a game at the same time.
I do want to help people get into GameMaker. When I first started I used to get stuck all the time, so if you have any questions feel free to ask and I will get back to you as soon as I can."
Includes dev logs.
Most recent tutorial or episode as of July 7, 2018:
6 months ago
VTR Studios
"VTR Studios is dedicated to game development and teaching, with a focus on providing high-quality Gamemaker tutorials. The studio also produces assets for the YoYoGames marketplace, and has a game in the works. Check out the channel for Gamemaker tutorials if you're interested in learning how to make your own games, plus keep up to date with whatever project the studio is currently working on!"
Most recent tutorial or episode as of July 7, 2018:
6 months ago
YoYo Games [sound familiar?]
"YoYo Games is the home of GameMaker Studio 2, the fastest and easiest to use cross-platform game development platform. GameMaker Studio 2 has been developed with usability and efficiency at its core, allowing developers to create games in a single code base and then publish them to run natively across an unprecedented number platforms including Android, iOS, OS X, HTML5, Ubuntu, Windows UWP and consoles. Together the entire GameMaker family of products have been downloaded more than five million times."
Most recent tutorial or episode as of July 7, 2018:
2 months ago ("Made with GameMaker").