Computer beginner needs help?

I am new to this whole internet thing. My kids know a lot more than me. Of course. The problem I have is too many things seem to be running in the background on startup. Making the computer slow. I have looked at various websites but am very wary of what is safe or not. All I want to know is how to stop some things running and explained to me in basic terms. Click here, click there. I have windows xp. And blonde hair to boot. That probably explains why I just don't get it. Please help if you can