I heard it was a great way to lose weight, particularly Ashtanga Yoga, but from videos I've seen on youtube, all these people look so skinny and thin... unnaturally skinny and thin.

I mean, I want to be thin but these people look, and please excuse me if this somehow offends, but they look like robotic aliens. I sometimes think these people are just bragging when they make all these poses in the beginner videos I've watched...

I was also wondering, can one just 'begin' any of the courses of yoga, like ashtanga yoga, or does one have to take a general course in yoga before trying any of the varieties in yoga?

Okay, these questions probably sound ignorant but I really don't know anything about yoga... so if anyone doesn't mind answering this poor guy's questions?

All I'll say from a few weeks of doing it....most painful experince in my life....

Aren't you suppose to take breaks for a few days? I've read that it should only be done 3 days per week.

I did >_>

Okay, so... what can you tell me about it? I'm hoping not to lose track of my original questions.

Is there any specific Yoga type that one has to begin in before trying the others?

it might be a good idea to google your questions -- you might get the answers you seek faster. 

Mostly, I think, it helps flexibility and strength. As in it's not the fastest way to lose weight, but no dobt helps in the long run.

I know a couple of people who do it for fitness (I think once a week with an instructor and like 20-30 minutes per day at home) and none of them are painfully thin. One of them is actually on the rounded side - but still can do a handstand.
I've never asked about the exact type of yoga they do since I have no idea about that as it is.

None of them do any of the other yoga stuff though, which includes diet and the yoga diet will probably leave you thin, it's something like vegetarian only with basically no overly processed foods, loads of sugar, oil etc... and never overeating, you get the picture.

Obviously, I've tried that already or I wouldn't be here. Don't assume.

So... no one? >_>;

I don't really know much about it, but apparently they teach you how to teleport and spit fireballs. Seems pretty cool!