A miner uses computational power to solve cryptographic puzzles for a Proof of Work (PoW) blockchain. As transactions are sent out to nodes in the network, miners collate these transactions into a transaction block. These collated transactions can be analogized to a page of transactions in a ledger book. The goal of the miner is to add this block of transactions, or page, to the blockchain, or global ledger.
Miner fees are small amounts of a cryptocurrency that are awarded to miners. The miner fees offset the costs (electricity, hardware, etc.) needed to process transactions on a PoW protocol, and serve to incentivize miners to continue solving those unique cryptographic puzzles. This allows for the continued creation and addition of unique blocks to the blockchain.
*Ethos will never charge you to send crypto from one wallet to another. However you may be required to pay a mining fee.*