Ethereum is a programmable blockchain that allows anyone to make various types of transactions between each other including sending cryptocurrency. Because Ethereum is programmable, developers can deploy smart contracts which allow for many interactions like lending and borrowing, swapping between assets and more.
Ethereum is currently a Proof-of-Work blockchain like Bitcoin. In exchange for transaction fees, miners can solve complex math problems using application specific computers otherwise known as miners to post transactions to the network. Ethereum is moving to a Proof-of-Stake consensus mechanism in 2023 which is more energy efficient and eco-friendly.