In Bitcoin you are the one who decides what fee you want to pay. All fees are optional (i.e you can pay 0 fee), however fee is something that rises the chances of your transaction to get into block (higher the fee - faster you can expect it to confirm). If you fee is too low - your transaction may never be confirmed since miners usually pick transactions with higher fees to include in block first. Usually fee is calculated depending on the size of your transaction message (in bytes). You can uread more on fees here https://support.earn.com/digital-currency/bitcoin-transactions-and-fees/how-do-i-calculate-my-transaction-fee