Suppose that you are the holder of 1 ETH, and the current price of ETH is $1000, and you would be willing to sell your ETH at $1500. You don’t know if the price will climb that high or not, but since you aren’t willing to sell it now — you can use it to generate some income while still holding ETH. You write a call for 30 days wi a premium of 0.2 ETH with a strike of $1500. You’ve just generated 0.2 ETH! And if ETH goes above $1500 and the long exercises the call, then you have just sold your ETH! You did miss out on the upside above $1500, but if you were willing to sell it at that level, you’ve just generated $1500 for your ETH.