Long position means that you are buying currency expecting it to rise with the intent of selling it afterwards. If you wish to buy a Bitcoin, for instance, then your account will grow in value as Bitcoin’s price increases. If Bitcoin price decreases, then your account loses value accordingly. You can enter the long position by executing a market order to Buy cryptocurrency at market rates or place a limit order away from the market. See an example of profit calculation for a 'long trade' here.