An ICO is an investment in the future of a business or technology.

Generally, a group of people will propose a project to build a technology or a business, and they sell the coins that the project will use. If the technology or business is successful, then the coins might have some value in the future.

ICOs are extremely risky. It is likely that most ICOs are just scams, and it is also likely that most of the rest will fail. And even then, the values of the coins for the few projects that succeed may never reach the value that you paid in the ICO.