MS paint is a common computer program, but is underrated. Here is how to make cool abstract art in less than 5 minutes.

[edit] Steps

Remember this can only be done if you have the MS paint program. It's usually installed on PCs running Windows.
Open Microsoft Paint. Go to the "start" button in the bottom left of your screen if you have a PC. Click on it. A screen should pop up
Click on "all programs" (may just say "programs") and another screen should appear. Go to "Accessories" and go down to "Paint". Click on it. You are now in MS paint.
Look at the upper left of the screen.

Place your cursor over the diagonal line icon (it should say "line").
Play around with the line tool and get used to it. Then draw different shapes (they should overlap), making sure that all the lines are connected (if you drew a square make sure there aren't any gaps in the corners). Leave space around the edges of the shapes.
After you finished it, it should look like a jumble. Click on the little paint bucket icon (it will say "fill with color"). Chose black as your color. Fill the area around the shapes in with black.
Go crazy. Using the paint bucket, fill in your shapes with different colors. The more contrast, the more eye catching.
Save, and show your friends.

[edit] Tips

Get used to MS paint. It helps to have a small amount of experience before hand.
You can try the other tools. See what blends. Remeber that yellow will look slightly different when placed next to different colors.