There are many ways to make money online.
Frankly speaking I have not made a dime as I have only gathered enormous theoretical information about making money online.
We can kind of classify the money making methods online into two
1)By selling products
2)By selling advertisement space as part of our content.
For selling products,we can use some online selling platform like ebay,amazon or classified websites like local selling.
After trying out to sell through these websites what I learned is that we can make money only if we select products with low buying cost & less postage cost.Since these website charge you for listing & Selling and adding to the postage cost,our final margin is very less.Either we need to sell products in volume or else sell products with high margin like electronic goods.What I suggest if you sell digital products like ebook,images..etc,they are downloadable online and there is no delivery charges associated with it.Hence you can make a lot of money out of it & avoid postage cost & have a care free selling.
The second part is interesting where if you are passionate about something & if you are easily overflow with words,then you can create a blog.As time goes on,People will get interested in your writing and if you get many eye balls watch your websites.You can place advertisement through google adsense program which will generate revenue for you.
Many people are successful in creating world famous websites and make good amount of money which made them to quit their jobs and make blogging as a full time career.
Now I see make good money by teaching in the online teaching websites like udemy where if you make a training video and upload it,it is automatically bought by students which generates revenue to you.