Fees are set by competition for limited block space, so they rise with congestion. They go to whoever produces the block, adding to the block subsidy as miner revenue.
As block subsidies halve over time, fees become a proportionally larger share of what secures a proof-of-work network, which is a long-running open question about Bitcoin's security budget.
This definition is educational and not financial advice. Crypto is volatile and high-risk — always do your own research.
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