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.
The beautiful thing about online is that you can decide to sell anything as long as you know you can deliver. Also, there is what they call drop shipping which enables you to even pull other stores and they do all the processing while your store is just there to monitor things locally and make sure it gets delivered. However, in terms of what to sell, it is always good to know what is missing in the community and what people would eagerly want to buy quickly... could be fashion, gym equipment, groceries, educational stuffs, and so on and so forth. All you just need is to find that thing and push it out to your target market.