If you already have a brick and mortar business and you are planning on expanding its reach to the internet, then you are off to a good start.
On the other hand, if you are starting from scratch, and an online website is going to be your sole moneymaker, then you have a lot of work ahead of you.
Your first step when creating an online business is to decide what it is exactly that you want your business to provide...
And who you want to provide those products or services to.
You need to attack a market that has enough of an audience to sustain your efforts in it.
For example: you might be super interested in Hissing Cockroaches.
Don't laugh: my roommate in college was (shudder).
Are there enough people in the world that are interested in that subject? Is it worth it to create products about Hissing Cockroaches? Only research will tell you the answer to this question.
As you do some research it will become clear that a lot of topics will not be very marketable for many different reasons.
For instance, perhaps there isn't really any interest in it or perhaps there is so much interest that the topic is saturated.
Saturated markets are difficult at best to break into and you should ask yourself if it's worth the frustration when there are so many good niche areas available to you.
So where to begin? How do you find a topic that will sell like hotcakes? RESEARCH.
Grab a pen and sheet of paper and make a list of all of the things that you enjoy, know something about, or are good at doing.
Take those results to Google and see what others are selling in those areas.
Take your time, do some research, and make sure that you talk everything through with your business partners and/or your immediate family members who may be counting on you to make the right decision.
When you have a general idea of which type of business you want to construct, and what product(s) you want to sell, you can move on to actually creating those products and the website systems that will support them.