The Bitcoin network reaches network consensus on its electronic payment system by leveraging miners’ computing power. Ethereum works the same way, it also gathers a network of computers, but to validate programs in a decentralised fashion.
Similarly to Bitcoin miners, Ethereum miners secure the network and get rewarded with new Ether.
The consensus mechanism has been following Proof-of-Work since inception, relying on both central processing unit and memory computing power.
Ethereum is planning to shift to a hybrid Proof-of-Work/Proof-of-Stake model via it's new version Casper FFG.
Rather than reaching consensus by mining or allocating computing power to the network, Proof-of-Stake cryptocurrencies select the next block creator in a deterministic way: based on their wealth and how much they are willing to stake (staked funds are “locked”).
The Ethereum foundation has not formally communicated on the date of transition to the hybrid model, although Casper FFG has been operating on a test net since early 2018.