Welcome aboard!
Areas are easy: most folks use Folders to represent them in OmniFocus.
Tags: OmniFocus takes a different approach to categorizing your actions than Things does; both approaches have strengths and weaknesses. Tags let you be a little fuzzier in how you define your actions, but that means you have to think more about what you're looking at actually means.
There's some good info in a
previous thread started by someone switching from Things to OmniFocus. There's some particularly good advice from our CEO on pages two and three.
(Posts
#14 and
#15, in particular, though there's some good stuff on page three, as well.)