Having decided one day to start your own selling business, you will come up with question "what to sell?". 
But right before to decide what to sell, you will have to answer another question "where to take staff to sell?" Well, there are three places to find staff to sell.
First, you may create something by yourself. Second, you may buy something and resell it. Third, you may make up something abstract to sell.
I don't think first two options attract you a lot. Maybe because you don't have storage place for products you want to resell. Maybe because you don't want to invest money in buying staff to resell. If you have storage place and money to invest, stop reading this book, just open regular Grocery or 99 cents store.
But if you don't want to think about storage and start capital then your option is third.
There are millions abstract things to sell in internet. Just to remind you... Abstract thing is a thing which you cannot touch. Though you may find different definition what is abstract in dictionaries. As for me, any noun without physical body is abstract.
There are low cost and high cost abstract things you may sell. 
Low cost includes downloadable products as ebooks, songs, movies, clips and so on. You may create something once and sell million copies for the price of one dollar.
Low cost products are not part of this tutorial. This tutorial covers high cost abstract products.