How do you get weapon cases and other stuff you can use to win something
You can either buy cases or weapons from the market place or get them as drops ingame
Do you need anything else to open them
You need a key,which you can buy in game menu,you can't get a key as a drop.
Can you sell your case drops
Yes,you can sell your cases or weapons to the market place.
Why can't I trade anything at the moment
"We require that users make a purchase on Steam in the last year, the first of which must've occurred more than 30 days ago.",basically you haven't used market place in a long time,you'll have to wait a month,might be a diff problem for you,but for me that was the case,or if you log in from diff PC it will be a week.
Does selling some CS:GO stuff give you money in your steam purse?
Is there any other way to get money into the steam purse, apart from paypal or credit card? Because I do not own any at the moment.
Yes,selling ingame drops.You can sell your csgo items and it will go to your purse.
Is it normal to see an enemy in radar in CS:GO?
Yes.
In many CS:GO servers, why do I get a connecting problem regarding VAC?
what kind of a message you're getting?do you play competitive or community servers?
here is a a site regarding all the cases weapons etc etc on where you can obtain them from and price.
http://csgostash.com/