555 Timers are a great intro to electronics, so I thought I'd throw together a quick guide on how to set up a simple flashing LED, as a sort of "hello world" project.
555 Timer pinout:
Construct the above circuit, plug it in, and watch your LED flashing! To adjust the frequency, you can vary the potential divider, in this configuration, it's about 2Hz. It works by using the IC as an astable multivibrator, and just sticking an LED on the output to show it. There's a pretty good explanation of how it works here.