If you are able to get free lance work and a client who can trust you and give you a mini contract then trust me that you are in that online business whether it will be seo or data entry.
To start any online business one should have prior knowledge about the business want to set up online and also have the knowledge of online business policies and all other key skills that one has to develop on its own.
Freelancing, entrepreneurship, consulting, reselling are some of the booming startup ideas. Along with all this you can also go for SEO, SMO, PPC, Affiliate Marketing, data entry & many more.