From a very high level, a Web flow is just like a wizard in a stand-alone application. It guides a user through several steps of interactions. Complicated wizards may branch out depending on the information entered in early steps, so do the Web flows.
Well, Web environment has its uniqueness and challenges. Spring Web Flow is designed to ease it. Like any other framework, you have to overcome the learning curve before you can really take advantage of it.
The good news is the Web Flow still fits in the MVC framework overall, just with a new set of handler mapping, handler adapter, plus the new flow executor.