It sounds like you did a clean Windows install. Windows has drivers for many hardware devices, but not all -- for those it does not, you will have to download the drivers. If you have some discs that came with the hardware when it was sold, that will work too.
One of the missing drivers is probably for your network card, so that would explain why you can't connect to the Internet.
Your main issue will be that you probably don't have any clue what drivers you need. If it's a namebrand computer (e.g. Dell, HP), go to their website and look for drivers for your model. If it's not, download and run
this to identify your motherboard, then check the board manufacturer's site (or post the board model here and someone can point you to the right files).
That should take care of everything integrated on the motherboard, which hopefully will be everything you need. If you have any add-on cards that are not recognized, you can ID those by taking them out and looking for names and model numbers printed on the cards.
