Legacy GM Platformer slopes and non plain floors and how to use "Applies to: Other"

[Ziliock]

I want that when the player walks it finds for collision-free space to move in the floor.How can I make that with only a few actions?Previously I tend to check every location to make that.Like:If x4,y-2 have collision go to x4,y-3 and if x4,y-3 have collision go to x4,y-4.
And what makes the "Applies to: Other" thing in the actions menu?Can I control it with blocks?
In drag and drop if it is possible please