Ecommerce websites let you sell your products directly to customers. You just need to set up a website and add your products. Customers can make purchases and you can deliver your products directly to your customers.

Even though most famous brands sell their products online, small businesses are a little bit far behind selling their products online. Most of the time this is because they don't know how to set up a Website or cannot afford the cost to set up an e-commerce website or they don't know the process involved.

Yes. It costs money to start selling your products online. But here is the thing. It costs money to set up a business offline also. There are infrastructure costs which are very High and Electricity, office maintenance, etc costs more than the cost involved in setting up an online shop.

Let me break down how does a simple business can run online. 

The first thing is you need to have a website, it should have features to add & manage products, receive orders. 
Once your website is ready you need to have a payment gateway, which lets you receive payments from your customers (PayPal is a famous payment gateway).
After that, you can start marketing your website to get customers.

You'll receive orders, which then you have to fulfill by hiring a courier company which can deliver your products to customers, depending upon the cost of the product you can charge the Delivery cost to customers or you can pay it if the product is costly and you earn very good margins.

So that's it. It's a very easy process to implement, once you familiarise yourself with this process you can improve how your business requires it.