You need to port forward not only on your router but on your modem as well if your wanting people on the outside to join. steps to portforward to the outside.
For modem 1st:
[I would highly suggest making your computers ip static to make everything easier]
1. type 192.168.0.1 into your browser(if thats your modem ip)
2. enter password and username if needed(default ones can be found online eg either user:admin pass:admin or etc. or you can reset it if you forgot it, same with the router)
3. look under portforwarding or like mine under services add the port and ip[routers ip] you wish to forward. minecraft is generally 25565 unless specified differently. do this in both udp and tcp.
4.do the same steps with your router but to access your router type 192.168.1.1(if thats your router ip) and under portforwarding add your computers static ip instead.
5. check your modem ip at
http://www.whatismyip.com/ users will use this to connect to you or if they are local in the household they can use your computers static ip that you specified as well.
If its a little hard to understand, a basic example is this
oip=outside ip address
iip=inside ip address
oip[
www.whatismyip.com/]-->Modem iip[192.168.0.1]
oip[192.168.0.?] {set static} -->router iip[192.168.1.1]
oip[192.168.1.?] {set static} -->your computer
modem forward: ip=[192.168.0.?]{static router ip} port=25565
router forward: ip=[192.168.1.?]{static computer ip} port=25565
If you are wanting to have people connect from across the internet I would highly suggest getting a free dynamic dns as your modems outside ip might be dynamic and constantly changed by your provider.
