m0n0wall Forum - How does the routing out through WAN work?

Just curious, does M0n0wall have some default-route entered that points everything out the WAN?
Or doesn't it have anything like that at all, instead getting default gateway from ISP's DHCP (or entered manually for those ISP's that have it that way)?

Just wondering how it works. Cause if you got two LAN-interfaces, somethings gotta tell the router to put traffic intended for unknown networks out the WAN.

Also, more theoretical and maybe even stupid (sorry), if you have two private LAN's, directly connected to the router, and a client on one network tries to visit a webserver on the other network....if you dont run any NAT/PAT or anything since its just internal anyway, do you need to open firewall both ways?
Or can you just open destination port 80 from the "asking" side and it will fetch the traffic from the webserver-network even though all ports are blocked from that side back?
Thought maybe that kind of stuff only works when NAT/PAT is running and if not you have to open ports backwards too....oh well, its something that went through my head right now Cheesy

Thanks