This is a loaded question. Be careful who you ask. There are tons of scams out there.
The easiest way to make money online is to sell something. The hard part comes down to marketing.
There are two basic ideas for marketing
1. Hire someone to manage your social media and take care of you public relations = paying money
2. Tracking your keywords, blog post, social media and anything to get the word out that you are selling something = free but your time is payment.
If you are not selling something, then you are working for someone who allows you to work at home using a computer. This is dangerous as well because you could work your tail end off and then not get paid.