Did you know you can see everything your computer is doing at any given second? Open up the Windows Task Manager by pressing Ctrl + Shift + Esc. Click on the Processes tab and you'll see a list of every bit of active code.
Unfortunately, most of it will look like gibberish. What the heck is csrss.exe anyway? (It's a critical process that stands for Client/Server Runtime Subsystem if you care to know.) But some of these processes aren't really necessary unless you're actively using the program they're tied to.
Unnecessary processes can slow down your computer, especially on startup. Some of those programs could even be viruses! But how can you tell the difference when all the names are in what seems like a foreign language?