It used to be easy a decade or longer ago. Not so easy now. There are many ways to earn income on line, but mostly, it takes years, a lot of trial and error, and by the time you've learnt it, that is no longer a way you can earn money.
Basically, like all businesses, you have to look at how much you want to earn, then look at your skills, then decide whether it's doable.
Sorry, your question is broad. There are too many variations to cover in a simple response.