There are lots of ways to make money online and selling things is one of those ways. It can be a lot of fun and fairly easy if you know what you are doing.
Firstly you will need to think about what you are going to sell. Do some research and see what other people are selling and what seems to sell well. Find out how much they are selling for a research whether you can buy them cheaply enough to make a decent profit. Consider how you are going to compete. Alternatively you could look for a gap in the market and try to fill that. See whether you feel there are products that people want or need and that they cannot buy online and see whether there is a way for you to get hold of them and sell them.
Once you have an idea of what to sell, you have to think about where to sell them. There are quite a few options and you can consider whether you want to try one of them or several. You could set up your own website and sell through there. This might be the cheapest option if you are able to design the site yourself, but you will still have to pay for hosting and a domain name. You will then have to promote the site so that people can find it. This could also be costly, although there are free ways to do it. Alternatively you could sell your products on a website that has already been established. This means that people have trust in it and so they might be more likely to buy things from it. However, they will charge commission on sales, or fees to list on the site and so you will have to take these costs into consideration. These days a lot of people choose to sell on social media. There are some groups that you can join to do this, some sites have marketplaces or just through a profile page. Most of these places have no charges for selling, but the amount of people that see it will be more limited.
Making money can seem easy but many people forget to take the very basics into consideration make sure that you add up all of your costs and then work out how much you need to charge to make money. It is easy to have very small profit margins and then end up with very little money to pay yourself. The thrill of selling things can get to be so much fun that you actually forget about the fact that you are trying to make some money. You will need to make sure that you can make enough money to cover your bills etc so you need to choose products that you can make a decent profit on and therefore make enough money from. Make sure you research first so that you are confident that you will be able to make money from your idea.