1. When you first register, you are asked about your chess skill level... beginner, intermediate, etc. Different answers give you different starting ratings.
It makes almost no difference. Your first half-dozen games should be enough to move your rating close to your actual skill level, and from then on you'll be facing opponents near your own strength and winning about as often as you are losing.
2. Don't know, but as I said your first few games will adjust your rating by hundreds of points... only after you have played dozens of games will the win/loss adjustment drop into single digits. And the number of points you earn is multiplied if your opponent is higher rated.
3. Way too many factors involved. The difference between the ratings matters. If you lost to a player rated hundreds of points higher, it might cost you only one rating point, or even zero. But if you had somehow beaten him instead, you might earn a hundred points! The statistical signifigance of your rating (called rD) is also a big factor. A high rD (means approximate rating) will mean lots of points won or lost, while a low rD (means accurate rating) will mean much fewer points change hands.
4. You lose exactly the same rating for a loss, no matter how it happens. It is considered very rude, however, to just sit there and refuse to EITHER move OR resign... just making your opponent wait until the clock runs out. That's called "stalling", and should be reported to chess.com.
1. Why do some people start with 400 ELO like me, some with 800 (like my friend) and some with 1200 elo. I know that it shapes as you play, but why?
2. Let's say I am a 2500-rated chess player (FIDE) and I don't want to go from 400 ELO to 2500. I know that you have to send a picture with some info on a sheet of paper before they give GM title or any other title, but do they (chess.com) adjust your ELO or not?
3. How can I calculate how much ELO would I lose/get if I win/draw/lose with a certain player?
4. This is the last one I promise. Does it matter if I resignate or get check mated or do I lose the same amount of ELO each way?
Thanks to anybody who knows the answers to my questions and decides to waste his time answering them.