if you have no idea what you want to start with or you only have limited product, probably you can consider to make it like online market place, people can sell their product through your website and at the same time you can sell your own product as well.
It's good to have this type of market place and it will attract a lot of merchants to sell with your platform. Just like what's with dropshipping, if you do have an idea like this with oberlo / shopify you can earn great with this. But today I'm still trying to know things about this business and just like what others doing now, I'm trying my best to acquire a lot of information, tips and help to start my own online shop.