Check out more student examples here.
Click and drag out your canvas so it's about 1000 x 1000 (make sure you see all of the canvas at 100%).
Zoom in to 500% using the slider at the bottom right of the window.
Select the Rectangle tool
Draw out a rectangle/square (by dragging while right-clicking) with lots of room around it.
Set the Selection tool to "Free-form", making sure transparent is checked.
Select a part of the left side of the shape, making sure you use the entire side. Start outside and end outside the side of the rectangle!
Move the selection using the right arrow key to the other side. Make sure you don't use the mouse or go up/down at all! Then click off.
Repeat the previous procedure, selecting from the top and sliding to the bottom (or vice versa).
Make your shapes unique - add eyes or other details with the Pencil or Brush tool (so long as you stay totally inside your shape, not touching the edge at all).
Select with the area that's completely filled with shapes, no white spots, then use the Crop button.