If I have 0$ at the moment can I make 100$ in 2 or 3 months? How?
What if I deposited 20$ .. Can I make them 100$ in less time?
If your starting from $0 then you'll have to do some work to get the initial money. You can work in signature/bounty campaigns or you can charge for any skills you have such as marketing, programming, etc. If your starting with $20 and you want to trade, you can definitely make $100 in 2-3 months but you can just as easily lose that $20 in the same time period or less.
if you have skills that you can sell why not? there are many users in this forum who have skills in graphic design they can sell services for logo design, signature, or the like. or you have skills in marketing you can try signature campaign and more. the most important skills you can sell dude