Ethereum in its current state is using proof-of-work (PoW) to ensure consensus amongst the thousands of nodes in the network. While PoW is reliable and secure, it is also extremely energy intensive. To produce each block on the network participants are required to use powerful and energy-hungry GPUs to solve a complex mathematical problem.
Alternatively, proof-of-stake (PoS) guarantees the security of the network in a different way. In PoS, anyone with 32 ETH can deposit that ETH to become a validator, a node that participates in the network's consensus algorithm. Finalizing a block requires 2/3 of all active validators to sign off on it. Should a malicious actor try to tamper with the underlying protocol by using a large number of validators to revert a finalized block (the equivalent of a "51% attack" in PoW) their funds are slashed — meaning they lose a portion of their staked ETH. This makes attacks extremely expensive; it would be like a PoW system where if you use your mining hardware to attack the network then your hardware catches fire and is destroyed.
PoS does not require the same energy-intensive hardware as PoW. Any relatively recent consumer hardware should be capable of running the software required to operate a 32 ETH staking node. If you deposit more than 32 ETH, you will be assigned multiple "validator slots" by the protocol, but you will still be able to run them from a single computer, though hardware requirements go up the more you stake. Most estimates put the expected energy savings from the switch to PoS to be around 99%.
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