
In crypto currencies markets there are 2 types of exchanges. The first one is spot exchange (you buy real bitcoin) and the second one is a derivatives exchange (futures market). In the spot market in order to buy one bitcoin you need to deposit fiat currency (EUR,USD etc). But in the futures market you can speculate about the bitcoin price or other cryptos, depositing bitcoin as collateral. The value of the collateral will increase/decrease with the price of bitcoin.