A cloud miner is a highly efficient computer specially designed for
cryptocurrency mining. In cloudmining datacenters are hundreds of miners.
You can buy whole miners or mining power like you buy a webspace for your website.
The mining computer are connected to pools like (Bitcoin mining pool, Ethereum, etc)
You can choose which pools you want to invest and help mining in this pool with your own hash power.
Usually the mined cryptocurrency is distributed among all customers of the cloud mining service
(i.e. hashflare.io) depending of their hashrate in the whole system.