Some blocks in Game Lab have inputs, or parameters, that aren't used every time.
When you first used the rect block, it always created a square with sides of length 50. It had two inputs that you could use to specify its x and y coordinates. rect also has two more optional parameters. These parameters are used to specify its width and height. You can use the arrows on the right hand side of the block to show or hide these optional parameters.
Ellipse also has optional parameters for its width and height after the x and y parameters. You can show or hide these optional parameters with the arrow on the right hand side of the block, just like with the rect block.
Found a bug in the documentation? Let us know at documentation@code.org