Port Forwarding for FTP server

I'll get straight to the point. I recently set up a FileZilla server to get all my files anywhere to watch or access. I have already set up the user and directory I want to access, as well as picking the port. The problem is my NAT router. I have put exceptions in my firewall on both machines for the port I used (7780) and I have set my passive mode to get my exteal IP from the filezilla site, which I heard is supposed to help me, but I can't coect to the machine using my exteal or inteal IP's (both coected to LAN). I have tried to forward the port to that IP, but I think in doing so I lose the ability to coect within the network because all traffic even going from the machine forwards back to it. Here's What I need to know:

• How does the passive mode work?
• How do I configure the ports to forward to that machine while still being able to coect to my server within my household)?