load codes are one of those things that can't really be explained very well if you don't already have some idea of what needs to be done. they basically just involve matching items and numbers to letter combinations. for example say my hero is level 66, so let the letter A represent the first digit (1 if you will), and the number 3 represent the second digit (30) so what we have is the combination A3, which in my made-up base 36 number system represents 66 since 1x36 = 36 and 30x1 = 30, add them together and you get 66.
alternatively you could use a simple base 10 number system if you don't understand the concept of alternative number systems, however you won't be able to store nearly as much information and your codes will be easily hacked. say, as in the above example, you want to store a level 66 hero with a sword of awesomeness. just store the hero level as it is: 66, and let the number 35 represent the sword of awesomeness. so the load code is 6635. you can add more digits to this code depending on how much information you want to store.
load codes are easy if you know anything about alternative numbering systems like base 2, base 8, base 16, etc; they just end up being a lot of busywork. my own load codes involve base 600 (-.-) which saves me a lot of space and makes it nearly impossible to hack my codes. if you don't understand the concept, however, you're in for a rough ride.