General Networking Questions?

Ok, so I am good with computers in general, but my weakness is Networking by far. so……..

1) We had someone set up our network for us, I have no idea how to add a comptuer to my network when I can see my network in “view workgroup computers”.

2) I want to set up a server for everyone to be able to save documents on it.

3)Is there any way to combine two networks in the same house to act as one?

4)If I am hosting a website, is a switch safer to use than a Hub?

I need to know how to do everything in the list above, PLEASE HELP ME!!!

thanks!

P.S. Can any of you explain, somewhat in detail, how i would do everything above

I know nothing about networking .Does having one or more of the Cisco certs i:e CCNA , CCNP OR CCIP , actually gaurantee a decent job ?Which certificate/skill is in highest demand ?