How do people actually make money from an online store?

By selling repeatedly to people they already acquired. Almost every store that earns a living does it on the second, fifth and tenth order, not the first.

In more detail

The first order usually pays for the advertising that produced it and not much else. Everything after it is close to pure margin, which is why two stores with identical revenue can be at opposite ends of profitable.

What to do about it

Selling online is not passive income. It is a business with stock, customers and a support inbox, and anybody describing it as passive is selling a course.

The number that decides whether a store works is not revenue, it is what is left after the cost of the goods and the cost of getting the customer. Plenty of stores with impressive revenue make nothing.

Repeat customers are the whole game. Winning a customer costs money; selling to them again costs almost nothing.

The mobile app angle

This is where an app earns its place — it exists to make the second and third purchase easier, which is where the profit is.