From what I've read online those make money by posting ads online jobs are scams or very worthless in terms of earning any decent amount of money for the time involved.
A better way to earn money would be to setup a blog and blog on a topic you know a lot about and are passionate about.
Then when your blog gets enough search traffic such as 1,000 or more daily unique visitors then promote affiliate ads or even use Adsense on the website to earn some income.
Some people earn thousands per month with a blog and affiliate ads or Adsense ads.
You just need lots of great content targeted on the correct keywords that will get you lots of search traffic to earn the money through blogging.
It can be done but takes a lot of hard work in the beginning.