To start a business and get income from it, you need to consider market.
What is market
The term of market cover any virtual or real area that verbs of purchase and sales will be happend. Any thing could be buy and sell in markets.
For example, if anybody put some books on a table beside a street and show them to pedestrians to sell them, so that it is a small market of books.
How to consider the market
To find the best items to sell in the matket you should pay attention to ask and bid rules in the market.
It means you should discover what people need to have in their life at specific time.
For example in about 5 years ago mobile handset, Nokia 3100 is the most wanted item but nowadays Samsung note 8 is the most wanted item. So, if you want to sell better you should offer note 8 replace of Nokia 3100.
It is a ask and bid operation to sell better.
Also when you found the best item, you should plan how to get money from buyers regards to current economic conditions.