You have a 100 rupees. It lies in your pocket for a year and still remains a 100 rupees at the end of the year.
Now, instead of your pocket, you decide to put the 100 rupees in a bank fixed deposit. The amount grows and becomes 105 rupees at the end of the year (assuming the bank gives you 5% interest).
The decision you took of changing the location of your money is what investing is.
There are numerous places (investment avenues like shares, real estate, gold etc) you can allocate your money to grow. Each of those have various pros and cons like risk, volatility, lock-in period and so on. Depending on what your circumstances are, choosing how much of the original 100 rupees to put into each is the art and science of investing.
This is an oversimplified explanation, but really, investing means not allowing your money to remain idle, that is, just lying in your wallet or savings account, because then you're not allowing your money to work for you by growing.