The easiest way to make money online for you is the way that you succeed with.
When that is said, there are many ways you can make money online. Some you have to invest more than others.
Either way you choose, you need to learn some skills and apply them.
If you think of easy as low cost, then making money as an affiliate would be a gret choice. Still you need to create traffic to the affiliate offer you choose to promote. Creating traffic can be done low cost or free, but you need to put in work to get a lot of visitors. To create traffic is maybe the single most valuable and important skill to learn in an online business.
Two great affiliate networks to apply for promoting affiliate products is Clickbank and Warrior Plus.
Lately there has been a surge of promoting via ads. Facebook is considered the king of paid advertising. Even if there is huge money to be maid using Facebook ads, most people tend to be unsuccessful due to spending to much, to fast, on poor ad copy.