Hi Elle.
When you visit a website certain info is downloaded to your 'putor. This info comes from many different sites/sources and is downloaded in some sort of order. Your 'putor relays back to the servers when something is downloaded, then the next one starts. (I think so anyway).
If you watch in the bottom left hand corner of your screen when you open a site you will see messages, eg: waiting for ????.com, followed by waiting for ??? etc.
Your computor is relaying information back to the servers that are supplying it.