question about network setup

[Nazar]

Alright guys. This is probably the complete newbie question, but I just cant
fight a straight answer on google. The questions usually I found, werent
answered. Anyways, to the point. I'm behind router. Cable modem -> Router ->
pc's. Basic home setup. I set up apache and want to figure out how is it
possible for me to use external ip to connect to my server? I can access the
server via internal ip & people can access it via my external, but for me
doesnt show up. I know this configuration has to do with my network, rather
than apache, or at least main configuration of my network and probably some
tweaking with apache....Well, if possible, some replies would be
appreciated. Maybe at least point me at the right direction. Thank you.