Investing just means doing something with your money with the hope that it will make you more money. This usually means buying something (an 'asset') that may give you an income, or you can sell the asset for a higher price (or both).

Investing can be done in lots of different ways, like lending it to someone and charging them interest, buying a house and charging rent/selling it for a higher price, or buying shares in a company and sharing in their profit or selling the shares for a higher price.