This is the game field. The game’s objective is to guide the colored boxes from Input to Output. There is a number of tools to aid you in this task.
Conveyor belts are the most fundamental components of your contraptions. You can create them simply by dragging the mouse while holding down the left button. You can change the direction of individual conveyor cells by clicking on them with the left mouse button. Clicking the right mouse button allows you to remove conveyor cells.