Transaction fees are included with your bitcoin transaction in order to have your transaction processed by a miner and confirmed by the Bitcoin network. The space available for transactions in a block is currently artificially limited to 1 MB (1000 Bytes) in the Bitcoin network. This means that to get your transaction processed quickly you will have to outbid other users.

The transaction fee is always displayed in Sats/vB. This means Satoshi per byte. So if a transaction has e.g. 1300 bytes, the following is calculated with a transaction fee of 50 Sats/vB: 50 * 1300 = 65’000 Satoshis (0.00065000 BTC)

You can see how large a transaction is on average and how busy the network is at mempool.

Transaction fees are directly related to the demand on the Bitcoin network. A block always has the same size and therefore cannot hold more transactions than intended. Accordingly, the fee is adjusted to the demand, as in an auction. If the fee is very high, wait a while until the demand decreases and then place your transaction.