The most used consensus algorithms in Ethereum are Proof of Work (PoW) and Proof of Stake (PoS). PoW was the first consensus algorithm used in Ethereum that was used in cryptocurrencies. PoS is another type of consensus algorithm developed as an alternative to PoW. PoS and PoW are developed for the same reasons but there are a few fundamental differences. In PoW, the validation of blocks happens according to the stake of participants.
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You can watch this video on how to mine Ethereum to know more about Ethereum: