If you want to use it on insanejournal or any similar site, you can use it in an entry by copying and pasting the code from the text box and editing in your own information. Anything inside the < > brackets is HTML code and if you don't know HTML you probably shouldn't mess with it too much. Anything outside is text and can be edited.
A good way to edit if you're not sure what you're doing is to use a code tester like this one from tessisamess. Paste the code in on the left and make your edits, and the result will show up immediately on the right so you can see right away if you make any errors or break the code.