You can make an object (or use another object, preferably your UI or HUD objects) and put some stuff into the draw event.
Some things like draw_text(x,y,string) Then of course if you have a real number that you want to display, you need to convert it to a string first by just putting string(bla) as an argument for the draw_text function.
Drawing like this is also useful because it allows you to visualize things better. For example, if you use collision lines, you can draw these lines out to get a better feel for things. You just put the same coordinates in that you use for collision_line into draw_line