No one can join the server/PortForwarding

Hi, I just started a Bukkit server. I set up the configurations, plugins, etc. but when I told my friends the IP address, they said they couldn't join. I was told to port forward the server, but I could not follow any tutorials due to my router user and pass not being known at the time. If anyone could tell me what port forwarding is, what it does, and how to fix my problem, that would be great. I will share the IP in 0's (for security reasons, each 0 is an actual number): 000.000.0.000
Thanks in advance!