Port Forwarding For Local Server -- Unable To Do It

These days I am experimenting with servers and hosting stuff so that I can learn how servers perform and how to keep them healthy. I have set up a test server on my ubuntu machine. I have installed the lamp package and tested everything (php, mysql, apache, phpmyadmin etc) and everrthing works fine. But in order to access the server through internet, I need to Forward port 80 to the computer hosting the server so that when someone enters my public ip address to a browser, the webpage hosted by the serveris made available instead of the login page of the router/modem (the 192.168.1.1 page)

I have never done it before and I have tried to solve it on my own but unfortunately I am unable to do so. So I decided to seek help from somewhere, and this forum was the first place that came into my mind (double benefit stuff.............)

The problem is that I have a Huawei EC5805 wireless broadband modem. It uses the CDMA technology to connect to the internet. It can be connected to a computer through wifi and usb. I use the wifi connection because I haven't been able to connect it to my ubuntu machine through USB (but thats another story for some other time).

The administration menu of this device, which can be accessed by visiting 192.168.1.1, is different than what tutorials online have mentioned for routers and modems. And this is the main issue because I don't have the basic knowledge of port forwarding and I can't find specific info on how to do it.

The menu looks like this:

The problem now is that I don't know what values to put into the fields. I know that port 80 has to be put in somewhere and that the ip address of the server is 192.168.1.100 but the rest of it is out of my head.

Any help would be dearly appreciated.

OK, seems rather simple.Your own server has LAN IP addresss 192.168.1.100.(simply check that this is a fixed IP address, will not change next week).The LAN port is 80.You will this LAN port 80 to be seen as WAN port 80 too.That's all, folks.I did not do this by myself, but should work that way.

And what should I select as the common port. (See the picture)

still port 80.