Proof of work is the consensus mechanism for blockchain to confirm transactions and add new blocks to the network and in return new bitcoins are formed which are given to the miners. It is what gives value to bitcoin.
Miners use computing power to verify the transaction by solving complex mathematical equations. There is a competition between miners to solve these equations higher the computing power is then there will be a higher chance of getting selected by Network. That is the reason miners join the mining pool so their hash power get increase and its easier for them to get selected by network and then the reward distributed among the miners who join the pool.
Miners actually transform electrical energy into digital weigh and get mined bitcoins and network fees in return.
Bitcoin proof of work model is a security measure that is a junction of cryptographic proofs. Proof of work makes the balance between the cost of expenditure and the overall bitcoin value.