-removed my attempt at explaining what to do-
I used this book to learn how to subnet, pics are 4.1MB each.
Class C (start with this one):
http://www.ultimateunity.co.uk/images/CIMG1830.JPG
Class B:
http://www.ultimateunity.co.uk/images/CIMG1828.JPG
Class B hand:
http://www.ultimateunity.co.uk/images/CIMG1829.JPG
Basically, you need to know how to do binary first. Then you need to know either how many hosts you need or subnets. Put your line in between this value and the one above it. Depending on how many bits you borrowed you can work out the subnet mask. (128,64,32,16,8,4,2,1 - add these up left to right until you get to your line.)
You need to work out your ranges now. You go up in your host values, so if you have 64 total hosts per subnet in a internal class C range. 192.168.0.0 to 192.168.0.63 will be the first one BUT this is your network address. It is not usable. the first usable one is 192.168.0.64 to 192.168.0.127. BUT it doesn't include these numbers. The first one is the network for the subnet. The last one is the broadcast address. The first usable subnet here is 192.168.0.65.
I hope this makes sense? If not I'll try again!