Gas Price and Gas Limit
Miners receive not only a reward for the mined block, but also the sum of all fees of all transaction that fell into this block. Therefore, it is more profitable for them to include transactions with higher fees in the mined block. That is why transactions, where the transaction fee is higher, are faster included in the block and, accordingly, faster confirmed.
On the Ethereum network, all transactions are performed by a virtual machine, which requires gas to operate. Therefore, the transaction fee is determined by two values: price and gas limit. The sender, as it were, says that he is ready to pay for the work of sending the transaction at "such a price", but at the same time so that "no more than so much gas is spent." Because the amount of gas required for sending does not depend on the amount of the transaction, it is more profitable to send transactions in which the price of gas is higher. The final transaction fee is equal to "gas consumed" x "its price."
For ordinary transactions (without data), the minimum required amount of gas is 21,000. For transactions on contract addresses, you need even more gas so that it is enough to execute the contract code. When sending a transaction, the maximum amount of gas that can be spent is indicated. If less gas is spent, then the fee will be less.
If you want your transactions to go faster - set the price of gas above average. The average (current) gas price is constantly changing depending on the network load. You can track gas prices in real time at ethgasstation.info
If transactions do not go away (not enough gas) - increase its limit