Moving Left & Right

Create a new object character. Set the sprite to the right-facing one.

• <Left>
• • Change Sprite: set to the left character sprite (don't worry about subimage or speed)
  • Check Empty: is just to the left of the character empty?
    (-4,0), only solid, relative
  • Jump to Position: (-4,0), relative

Duplicate the previous event for the <Right> Keyboard event. 

Open the Change Sprite action and change it to the right-facing character sprite.

Then change the X values to 4 for the Check Empty and Jump to Position actions. They should stay relative.

So your <Right> event looks like this...

Create a room - line the bottom with the main block object and place the character on the bottom. 

Test it out - does the character move left and right? If it does, keep going.