First, create a new document in Illustrator at 800 pixels by 600 pixels. Enable the Ruler (Ctrl+R) and turn on the grid on (Ctrl+"). Then drag a horizontal and a vertical guide onto the artboard.
We'll start by creating our shapes. Select the Ellipse Tool (L), and click on the center point of our guides. Then drag outwards by holding down the Shift + Ctrl keys. This will give us a circle that is centered on the grid/guides. Fill the circle with a red color (R=190 G=28 G=35) and leave the stroke empty.
