Patton's giving you good advice. Look at the CPU and memory usage, close some programs you don't really need running, and see if that lowers the usage of your resources. Rinse and repeat.
If you want to keep some programs from starting up automatically, you can use the msconfig tool (start->run->msconfig) to cut down on unnecessary programs when Windows starts up.
Now, if you're just wanting to know what the numbers mean, it's super simple. The ones that really matter are CPU usage and memory usage. Those two affect performance the most. Less use is better. However, this subject is can be a bit complex. If we haven't answered your question, I'm usually available through Steam Friends. Click the nifty button in my signature and I'll try to help you where I can.
-Xen