I want to start a raid in world of Warcraft but I dont really understand how to do it and what the benefits of doing it are. Ive pretty much just played the game by myself and never really done many of the dungeons or anything like that. I have a level 65 warrior if that helps at all. If anyone can tell me how to do it I would appreciate it.

You press O then you click raid then wait a while to see if people will join. The benefits are that you complete all the achievements then you get a prize like a black war bear. I think lvl 65 is to low for aiding a major city but if you want to do a dungeon go to Molten Core in the outlands

Some dungeons you can only 5 man it, which is a reg. party. A raid is when more then 5 people, do a dungeon that is hard and you need more then just 5 people to survive.
Some dungeons that are raids:

Onyxia's Lair
Zul'Grub
Molten Core
Black Temple
Theres more too (I prob don't know about the other ones)

Dungeons like Scarlet Monastary, Zul'Farrack, Scholomance are dungeons that you can only 5 man it. (theres more..waaay more)
If you want to start a raid, go to your char tab. (where you see what your wearing) and go to the raid tab. First of all you must have at least 1 person in the party. (it might be 5 people, but i'm pretty sure all you need is 1 person) then there should be a button that says form raid, or start raid, something like that. You can choose a main tank, main assitant, and raid leader. The chat for raid is /r and you must be in a raid to talk in raid chat.
Raid warning is /rw. You can do raid warnings in partys too. The main reason for raid warnings is when you want people to know something important.
Dungeons/ Raids that ur 65 can do:

Dungeons
Mana tombs (64ish)
underbog (63 thro 64ish)
Hellfire ramparts (60ish)
Blood Furnace (61-62 ish)
You can do Sethekk Halls. Its about 4 levels higher then you tho. (69ish)

Raids you can do:
Zul'Grub 60-64ish ?? bosses for me ( i'm lvl 70)
Onyxia's lair The guards are 63 I'm pretty sure. Onyxia (the main boss..duh lol is lvl ?? for me too.)
Molten Core (i'm not sure, but i think its lvl 60-65) some things are ?? tho.
Black temple is lvl 70+
Karazhan 68+
In raids/partys for dungeons you should have
1 tank
3 dps
1 healer

And remember, the main reason for raids are when you want to do a dungeon, but you need more then 5 people. And also remember some dungeons cannot be done as raids.

I hoped this helped
-grace