I'm a hobbyist programmer (with no formal education) looking to start doing small freelance jobs. One of the things that hobbyist programmers can get away with that those with a "real" job can't is lack of documentation. After all, you wrote it so you know how it works.

I feel a little silly asking because it seems like such a basic thing, but how do I document my code?

• How should it be formatted?
• How should it be presented? (HTML pages? LaTeX?)
• What does/doesn't need to be documented?

...And maybe more specifics I haven't thought of.

I mostly program in PHP but also C#.