The Movable Platform behavior will cause any object to become (a platform) to move in a specified direction. The platform has special characteristics that will carry any anything on top while it's moving.
This is the object that will be the moving platform. By default the current object is selected, but by tapping the graphic you can choose any other object in the scene.
The speed of the platform along the horizontal (X) axis. Negative numbers imply that the platform will move to the left.
The speed of the platform along the vertical (Y) axis. Negative numbers imply that the platform will move down towards the bottom of the screen.
This outputs the Object ID.
If you want your main character that's joystick controlled to be carried by a moving platform you can use this behavior. With this, the character can move freely on the platform as the platforms moves at the specified velocity.