If you want to do anything in the direction of starting an online business, I would recommend this book. Together with Personal MBA it forms the best introduction I can think of right now.
It is a short step-by-step description of finding, validating & launching digital products and an introduction on how to setup processes and automations so that you make yourself dispensible for a smooth business.
The focus lies on small businesses, called micropreneurship or bootstrapping, which can be done by one person or a small team.
This will mean you will target markets that are small enough so that you can target them with a small budget.
Definitly worth the read. I loved the no-bullshit approach.