To learn how to covert numbers to hex, first you need to know about what numbers really mean.
When you say 124 in decimal, what you're really saying is 1x100 + 2x10 + 4x1, or more correctly 1x10² + 2x10¹ + 4x10⁰. (If you're not using Netscape 2.0, this won't make any sense because you can't see my superscripts!)
When you say 124 in hex, you're saying 1x16² + 2x16¹ + 4x16⁰, or 1x256 + 2x16 + 4x1 which is 292 in decimal.
So, to convert a number from hex to decimal, just write it out in exponential form and add everything up. (That's what I did above.)

To convert decimal to hex takes a little more math.
Take your decimal number and divide it by 16. The remainder is the "ones" digit. Divide the result by 16 again, and that remainder is the 16¹ digit. Keep that up until there's nothing left to divide.

Example: Convert 292 in decimal to hex.
Divide 292 by 16: 292/16 = 18 r 4 (That r means remainder.)
Divide 18 by 16: 18/16 = 1 r 2
Divide 1 by 16: 1/16 = 0 r 1

Now there's nothing more left to divide. So look back at the remainders: 4, 2, and 1. Reverse the order of those, 124, and you have the hex equivalent of decimal 292.

Now, class, for homework I want you to do problems 1 though 658347 on page 49. You may skip problem 5.