I recommend that you start with a turorial to understand the basics of PHP. The manual is also a good place to learn things, especially if you know a function name but can't get it to work. Under PHP reference in the tutorial above there are more imformation about certain topics, well worth a look if you for example have a string problem.
If you need help I think that the best place to post is in newbies forum, if you want feedback on a code you have you should post in code critique.
