The units
SOL, the network's native coin, is divided into lamports, the smallest unit. One SOL is one billion lamports, so a lamport is a billionth of a SOL, similar to how a satoshi relates to a bitcoin. Fees are quoted in lamports because they are tiny.
The base fee
Solana's documentation states that every transaction pays a base fee of 5,000 lamports per signature. A typical transaction has one signature, so the base fee is 0.000005 SOL. The fee does not rise during busy periods, which makes costs predictable compared with auction-based fee markets.
The prioritisation fee
Users can add an optional prioritisation fee. The documentation explains that it increases the likelihood that the current leader schedules your transaction ahead of competing ones. In busy moments, such as popular token launches, a higher priority fee can be the difference between a transaction landing and failing. Wallets and apps set a suggested value for you.
Where the fees go
According to the documentation, the base fee is split with half burned and half paid to the validator that processed it, while the prioritisation fee goes entirely to the validator. Burning a share of fees reduces SOL supply slightly as usage grows.
What it means for you
Fees on Solana are normally a fraction of a cent, but you still need a little SOL in your wallet to pay them, even when you are sending another token. If a swap fails during heavy demand, retrying with a higher priority fee is the usual remedy. Always check that your wallet shows a fee before you confirm.