You may ask yourself why do I need to send fees, if the miners get the a reward when they find a block?
Because the reward of a block is divided by 2 every 210,000 blocks (Halving). This is what happened a few months ago, the reward decreased from 12.5 BTC to 6.25 BTC per block.
The miners can choose what transactions they include in their block. There is also no obligation for the miner to include transactions in his block, so it makes sense to add fees to encourage the miner to add your transaction in his block.
That's why your transaction is confirmed faster if you include more fees (the miners will prioritize your transaction)
Note: fees are also used for avoiding spam. In fact, if we can send txns for free, we can overload network for free, so fees are a way for avoiding that.
How fees are calculated?
What ultimately determines the price of a transaction fee is the activity level on the blockchain and the speed with which you want the transaction to be processed.
The more people who want to send a transaction, the higher the fees will be, because people will pay more than the previous transaction to get confirmed faster.
Fees can be calculated but it's not very simple... So the best option is to use websites like https://www.buybitcoinworldwide.com/fee-calculator/ or https://privacypros.io/tools/bitcoinfees
Thanks for reading
