Drew;
Simply type 'Find my IP' in the URL window at the top of your web browser (without the quotes) and you should see a bunch of responses but your IP should be at the top of the page.
The number will look similar to this format; 123.45.678.90 or 12.345.67.890 The numbers will vary but the format is the same.
As Dimus mentioned some but not all routers require port forwarding. It's essentially unlocking your router so that you can host. If you are not hosting or will never host then you don't have to worry about that part.
I hope the following helps. I know what it's like to be the noob and have all these questions about getting online etc, so hopefully this will spell it out and make things easy.
So to sum up......
1. Ensure each of your team (i.e. all the human players) have the same version of the game (if you don't it can cause problems). If you have a modded game, no probs, as long as everybody else has the exact same modded version of the game.
2. If you are hosting, you need to know your IP so you can pass it to your fellow players. They should NOT join the game until you tell them.
3. As host you start your game, go into Multiplayer and "Create a server" (you don't need to enter an IP at your end). You'll be prompted to name your session (call it whatever you want), select Dogfight (human vs human), cooperative (human vs AI) or campaign (same as coop but with a scripted series of missions forming a campaign). Select the number of human players (not necessary to be exact as long as the number is equal to or greater than the number of human players). Any aircraft not selected automatically are controlled by the computer.
4. After this you (the host) will see a small window "Mission Type" and a larger window with a list of "Missions". Think of the Mission Type as a list of books and the Missions are the Chapters in each book. You'll see what I mean.
5. Select a mission and click on "Load". You will see a pop-up with Standby and your mission info loading. Once it has loaded let your team know and then they can "join" (see the Join instructions below).
6. You will then be in the Mission Briefing screen with a map and an empty briefing window which will say "Choose a plane then check back here for your briefing".
7. Click on the "Aircraft" button and you will be in the aircraft/arming screen and will see a list of aircraft to choose and if all goes well you should also see your name, and your other players name at the bottom. Simply click under the Player column next to the aircraft you want and your name should jump up to that location.
8. Now click on the "Brief" button to go back to the Briefing screen and you will now see the details of the upcoming mission, your flight plan and the frontlines.
9. Once you have absorbed the mission info you have two choices;
a. Click on Aircraft and then Arming button to change your weapons loadout, your pilot figure (you can add your face to a pilot), your aircraft skin, how much fuel, which airforce etc.
Once done click on "Apply", then click on "Fly", OR
b. Click on "Fly"
10. You will then be in the "ready room" or ready screen. You will see your teammates' names come up as they finish selecting their own aircraft, loadout etc.
11. Once all your team shows up on this screen then click on "Fly". Your mission will load and start and you will find yourself in the cockpit. Start engines and off you go.
For your teammates who are NOT hosting but joining.......
1. Start the game and select Multiplay from the main menu.
2. Select "Join Server"
3. Enter the host's IP number (if there's one already there you can type over/delete it ) Ensure the dots are in the right spot and the :21000 is on the end
4. Click on "Join" (only when the Host tells you to) then you will see "Connecting to server". This may take a minute or two. If successful you will see an "OK" button. Click on that and the mission will load.
5. Go to Step number 6 above and follow from there to finish up (they will not see the "Fly" button in the ready screen, that's just for the host as he controls when the mission starts).
I hope this helps.
Possible errors to look out for:
1. If noone can join the host and players are "timing out" then it is probably the port forwarding issue that Dimus has indicated.
2. If some join and others can't, check that they have entered the IP number correctly, that's usually the problem.
3. If you are not comfortable with the port forwarding thing, before resorting to that have each human member of your team try to host and see if the rest can join.
4. Everybody has joined but one or more can't get the mission to load or get weird error messages. Ensure everyone has the EXACT same version of the game. If everybody has the stock game but someone has a modified game there will be problems. Conversely if everyone has the same modded game but one person has a stock game....same problem.
Finally.....if you don't have some form of communications such as TEAMSPEAK (it's free) then coordinating this becomes quite a chore.
Good Luck.