[Dovecot] noob - integrating dovecot with postfix

Hi list,

Just jumped providers and am now desperately trying to get IMAP running on a new server... But not getting the link between postfix and dovecot working. :-(

My two problems are:

1. local mail seems to get into the ~/Maildirs, but not from the outside (this is a postfix issue?)
2. I cannot find information on how to tell postfix to use virtual domains/addresses and then connect dovecot to them (as they are now in non-standard locations and/or formats)

I'm sure this is a FAQ, but cannot find an example that would walk me though this. Can someone kindly point me in the right direction?

-- Mitch