To draw a PRESET SHAPE in Illustrator, select one of the SHAPE TOOLS in your toolbar. (Don’t forget about the hidden menus for more options!)

After selecting a SHAPE TOOL, click and drag to define the size of your shape and release the mouse.

To draw a shape starting from it’s center, hold down OPTION(Mac)/ALT(PC) and drag.

To make a rectangle a perfect square or an ellipse a perfect circle, hold down SHIFT as you drag.

You can define your shapes numerically. To do this, draw a shape on the artboard with a SHAPE TOOL and click on the shape. A dialog box will appear that allows you to enter numeric values to define your shape.