investing in shares

When you buy the shares of a company, you invest in its business. As the company expands and grows and profits increase, its value increases.
This, in turn, drives up the value of the stock. So when you sell, you will receive a premium over (more than) what you paid.
It is not as easy as it sounds. A stock's price is always on the move. It could either appreciate (increase in value) or depreciate (decrease in value) with respect to the price at which you purchased it.
If you buy a stock for Rs 10 and sell it for Rs 20 after a year, your return from that stock is Rs 10, or 100%.
Or if you buy a stock for Rs 10 and sell it for Rs 9, you lose Re 1, or your loss is 10%.