Affiliate Marketing is the best way to start earning money online without investing money. basically you have to promote someone's product and if anyone buys from your promotion link , you will get commission from company , eBay , amazon and almost all the big e-commerce website provide affiliate membership without any fee,
Go to your social network profile and promote some product when they buy , you get money/ commission.
Example ;- make a unboxing video of any product and upload on youtube and give link (affiliate link) of product in the description and tell them " if you want to buy this phone there is a link below "