The documentation is mostly up to date. Some stuff is undocumented, though, and you might have to look at the source, but I would say at least 90% has some explanation. There are also various tutorials on the official docs that are current up to 4.0, though many have not been updated. However, it's not that difficult to look at an old tutorial and compare it to the new class documentation and make some small edits to function names, etc. If you need a tutorial to hand-hold you and you're just copy-pasting, then sure, you might have a hard time.
