Treeviews are really powerful interface components. I love building with them. They aren't easy to get started with, though, for a few reasons: they can't be bound to data so you have to fill them using VBA code, they're not part of Access and so aren't covered in the Access help (they're ActiveX controls), and they are often used with complex data, such as hierarchical relationships.
I started with some Micsrosoft articles and found that was all I needed to build my first few treeviews. Here are the two I used plus one more I've found since that looks like it would have helped me a lot.
As well as beginners' docs being a little scarce, the reference material can be hard to come by as well. Here's a link to the Treeview reference in the VB6 section of Microsoft's site.
See also: other treeview posts on my blog.