The easiest way to speculate is by buying a Call or a Put. As a buyer, you have the right to exercise the option.
If you purchase a call and the price of the asset goes up then you can purchase it for cheaper and sell it for its current price.
On the opposite side if you think the price of crypto is going down you can purchase a Put. If you are right you can sell that crypto for more than the current market price.
In general, you profit from the difference between your strike price and the current price.