CONNMARK howto

Hi all,
I'm looking for some docs to understand how to use restore-mark and save-mark in details.

Google search didn't help me: I found only simple examples, but I need to understand how use restore-mark and save-mark on traffic through a router (with lan and wan interface). I need to mark packets in PREROUTING on LAN interface because I need to filter by workstation mac addresses.

Thanks in advance,
Fabio