What is leverage?
In finance, leverage is the ability to gain and lose more for every unit of price movement of an asset. In this case, you can get a leveraged ETH (priced in USD) position which means that when ETH increases by 1 USD, you gain 1 to 3 USD of value (depending on how much leverage you choose) and when ETH decreases by 1 USD, you lose 1 to 3 USD of value.
As an example, imagine that ETH is worth 500 USD. You have 1 ETH. This means you start with 500 USD of value and without any leverage, if ETH increases in value to 750 USD, you will now have 750 USD in value. If instead your 1 ETH was at 2x leverage, then that same increase to 750 USD would result in you having 1000 USD in value. This is because the 250 USD increase in value was multiplied by 2!
Be aware, leverage cuts both ways. This means that if ETH decreases to 250 USD while you have that same 2x leverage, you will lose 500 USD in value (250 * 2) and you will be wiped out! Leverage is great when you believe that an asset's price will increase with time and you want to to maximize your gains when it does.