This is my first tutorial, ever. I hope you enjoy it!
Player Object:
1)Step Event: Check Empty X=0 Y=1 (only solid) and relative, start block, gravity: direction=270 and gravity=1, end block, ELSE, start block, direction=270 and gravity=0, end block.
2) Collision Event (with obj_wall): Move to contact direction=direction Maximum=12 (against solid objects), start block, vertical speed (no need to change it), end block.
3) Left Keyboard Event: Check Empty X=-5 Y=0 (against solid objects) Relative, start block, Jump to position X=-5 Y=0 Relative, end block.
4) Right Keyboard Event: Check Empty X=5 Y=0 (against solid objects) Relative, start block, Jump to position X=5 Y=0 (against solid objects) Relative, end block.
5) Up Keyboard Event: Check Collision X=0 Y=1 (against solid) Relative, start block, speed vertical -13, end block.
Game Maker Download: http://www.yoyogames.com/gamemaker/try