.. but I don't know where from. I basically have a BF3 with back to karkand. I am willing to get the DLC because I am quite interested in the first person tactical shooter. But as I said, I don't know where to start.

Instead of buying the DLCs one by one, a Premium account is preferrable.
You get all (coming) DLC with a discount, PLUS some small extras and
more events. In comparison with 6 months ago, the game works much better
and although there are hackers/cheaters around there are a lot of servers
which can provide you with hours and hours of fun. At ease soldier!

To begin with, I have no idea where is the multiplayer mode. I start the game, and I have NO multiplayer option

You need to select the Quick Match or Server Browser option in the web interface (Battlelog)

With the server browser you can select filters on the game type, location, map etc. Just pile in and have fun.

You might have the wrong disc in. The MP is on Disc 2.

Hi LeemzHQ! Is your BF3 soldier's name leem3322 by any chance????

Hi frinik22,

No, I don't have the PC version of BF3 (though I'm considering getting it). I have it for the 360. My gamertag on XBox Live is Leemz.

OK just a coincidence because I have a leem3322 on my list of friends in BF3....

Cheers!