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.
You can still join in the crypto world without any initial base but of course you need to find your own ways to get coin. But without initial base you can still join in airdrops, bounty campaigns and signature campaigns. This is free and anyone can join but you should pass the qualifications that require here.