The aim of these pages is to introduce the theory behind different processing stages. If you're interested in the practicalities of how to do an analysis, you might want the software page instead.
Below is an outline list of the areas of theory involved in functional imaging, and related documents that may help. Unfortunately some of these sources are difficult, but in my experience, all of them repay a slow reread, even if you think you understood almost nothing first time round. There is a bias towards SPM, but the same principles usually apply to other imaging packages.