Tokens are a means of ownership of the asset that you've been seeding / funding through an ICO that's listed. Think of it like a fundraiser that provides people tokens or gifts, such that once their service is up you can use those tokens to basically make use of the service. Once the service has some sort of value, this value is displayed on an exchange (A token exchange which is different from a cryptocurrency exchange), like for example an ERC-20 Ethereum token for ICO's that are based on the Ethereum blockchain).

Now, there are a couple of things here that determine the worth of the token and how they can be used:

There are a lot of medical based blockchain ICO's or blockchains built on top of the Ethereum network that provide some form of tokens which you can use to pay your doctors for their services or pharmacutical companies for the medicines that you buy. This is a very innovative use of tokens for patients. These tokens may be tradable for cash on an exchange that enlists it and vice versa.