Press <ENTER> to bring up the chat bar.

From there it's /a <your text> for ally/team chat. 

/w <name> let's you send a private message.

Use <TAB> to scroll through the options (/a and /w <names>).

/f sends a private message to people on your Friends' list.

And yes, you should definitely play this game in single player for a couple weeks before venturing online (which I find rather admirable).  The online multiplayer is lots of fun, but there aren't too many new players left, there are a large number of good players, and you really need to be good at the single player game before you're ready to come online.  Also, try to make a point of playing long games with each race so that you understand their tech trees and have a better sense of their strengths and weaknesses.  Also, spend some time browsing through old threads on the Strategy forum.

When you're ready to come online, be patient and understand that you're going to need to take your lumps and pay your dues in order to become good at this game.  Just stick with it, take pleasure in improving your game over time, and watch replays of the games and see what the good players do.  You want to try to reverse engineer your game strategy and micromanagement tactics by watching the good players.

Look forward to having you in the online multiplayer community soon.

Cya online!!

few of my general tips tho..

Start with FFA games first. Nobody can yell at you if your just expiermenting or you mess up.

Read up on what pugs are about on the forum

I have to echo what Centurion says about taking your lumps.  I played my first public 4 or 5 online matches yesterday after practicing with my buddy and we got whopped on pretty bad, lol.  Instead of qqing about it, we just watched the replays and discussed what people were doing.  It was a good ole time and I learned a lot of tricks.  Especially in the replay with JohnJames when we were double teaming him and he still managed to win :/ (with an ally feeding)

If you're playing on windows, push Alt + F4.

Just kidding

Everyone has pretty much covered the chat, but I would also suggest having fun renaming ships and planets when you can afford the chance. This gives you a good way to have some fun even if you are losing.

Case in point: Last night, before we started the match (2v2), we had a discussion about smilies since I didn't know how to make the crying smiley without clicking on some icon. Later in the game, my partner (purple) was destroying the guy next to him (red), so he (red) renamed all his planets to

We all had a good laugh about it.

PS You can rename a ship by selecting it and clicking the orange button above it's image on the bottom menu bar. There's also a hotkey combination, I think it's Alt + Y but don't quote me on it. I still don't know a good number of hotkeys.

Thanks for the rest of those tips. After looking at some froums and posts, I decided how to approach multiplayer. The first time...psh...wipe out. But after looking at some strategy posts and tips, I tried again and did okay. I also like how the people on here interact. Everyone is willing to help out the newbies (such as me). Cya all online!

Oh I do - because I know how useful it has been since I learned it