You can earn decent money from online if you have either one of these,
1) A Youtube Channel - no investment needed.
But you may need a camera if you are going to record videos and you may need to know video editing which is not a big task. You can either use free or paid video editing software. Youtube channels are easier to get traffic than a new website.
2) A Blog or website - some investment needed.
There are free hostings and free subdomains to start with, but they won't attract traffic. You have to write articles and the article topics need to attract search engine visitors. You can use WordPress, Joomla or Drupal. If you only want to build your site custom then you have to pay for the development.
3) Mobile Apps - more investment is needed than the above 2.
You can also earn from mobile apps but people only install very few apps on their mobile. Your app has to be really good to install. Developing an App will also cost you unless you can do it yourself.
4) Freelancing - You can do online works for others.
5) Selling your own products - You can sell WordPress themes, codes, plugins, computer hardware, or any other product which you can produce.
6) Domain reselling - Buying domains and selling it to domains.
7) Affiliate marking - You will get a commission for people buying things from your links.
8) There are other ways too.