We did a specific thread here in the forums on Sitepoint about positioning and contains many many useful nuggets of information for both beginners and advanced.
Just look through the examples and read the thread and you will find most of what you need to know. Some of it is complex and some straight forward but all useful in learning the finer detail of positioning techniques.
CSS isn’t hard but is not always easy to know which approach is right when you can accomplish the same thing in many ways. Context is the key which is why we often posters to elaborate a bit more about what they want when they ask a question although some posters get disgruntled when we don’t first give a direct answer (as in a recent thread 
).