Just like any currency. You can sell your services or products for crypto currencies and this will allow you to earn crypto. This is the whole point of crypto currencies. The fact that not everyone is ready to pay for goods or services in foreign cryptocurrency, but such buyers still exist and their number is gradually growing. As a last resort, you can exchange the traditional money for crypto currencies, that in some way it will be possible to consider that you have earned crypto currencies (except for the intermediate stage with the conversion).