Network Cables and Connectors For Sale

The simple differences between Cat 3, Cat 5, Cat 5e, Cat 6 cables...

How to create a LAN network for 1 room consisting of 20 computers, need them all connected, a working topology they can use (most likely star topology) and a switch, and I think, a server too (money no object)... Need to explain, describe and justify the choice of each hardware & the chosen topology..

Many thanks for your help, I did a Level 2 General course and when I moved onto Level 3, I switched to the System Support section.. I'm in the deep end now haha... I've only been learning about computer networks for a month.