Longing crypto can be done by buying Bitcoin on the exchanges and selling it when the value rises. However, a more advanced and profitable way to long crypto is to use margin trading on an exchange.
When longing via margin trading, one will have to put up collateral to borrow money and use it to purchase more crypto. The advantage of margin trading for long trades is that they can be exceptionally profitable, however, it does come with a certain risk.
As for shorting crypto, margin trading is the easiest and most widely-used way to do it. Benefiting from both rising and falling prices makes shorting a more flexible strategy.