First you have to choose a business model.

Before starting online business, there are several different business models to consider.

Dropshipping

It is the darling of e-commerce world. Why? Cause its the barrier to entry is so low. You don't need to make any financial investment to get started. Means, you won't pay until you make a sale.

That means you dont need large order or store stock.
Here is how Dropshipping works:

1. A customer place an order to your online store.
2. You placed an order to your supplier
3. Your supplier packages and ships it directly to your buyer.

Wholesaler

This is more traditional retail business model. Once you decide on what's product you want to sell, you find a realible wholesaler and buy the products in bulk. It requires a significant cash to spend up front. The upside is that you can get it way cheaper than dropshipping. Meaning, higher profit if you make a sale.

Sourcing from manufacturer

It is similar to sourcing from wholesaler the difference is that you can work with the manufacturer to create your own products.

Initial investment is higher as you are creating new products, so if you want to brand and sell a unique product then sourcing from a manufacturer is the business model for you.

Making your own products

If you have a unique skill, creative and artistic skill, then you can make your own productsand sell them online. You can even start selling it as a side hustle, while still working. And if you get successful, you may turn it into full-time job.

Main thing selling your own products is that you shoulder all the responsibility. You can only sell as much as you make. Aside from cost of the item you're making, you don't have to invest upfront, is the benefit of it. You also don't need to rely to suppliers.