You're mixing up bitcoin's and ethereums terminology. Eventough this isn't a big problem, it might make things very confusing for newbies. Ethereum is using the terminology 'gas', bitcoin uses the terminology 'fee'.
When you create a bitcoin transaction, you use one or more unspent outputs that fund an address controlled by your wallet. You use these unspent outputs as an input to create a transaction whose newly created output output funds the address provided by the person you're paying.
When you take the sum of the value of the outputs, and substract the sum of the value of the inputs, you get the fee.
When a miner decides to add your transaction to the block he's trying to solve, he can add the sum of all fees of all transactions in his block to the coinbase reward. So, the bigger your fee in relation with the size of your transaction (in bytes, not in value), the more incentive a miner has to add your transaction to the block he's trying to solve.
Soooo... If the person who created the transaction used a fee that is lower than the recommanded fee, there is a big chance you'll have to wait for a long time before your transaction finally ends up in a winning block. While your transaction isn't included in the blockchain, it usually resides in the mempool of the nodes. Most nodes have a setting to prune unconfirmed transactions after a couple of days.
If you transaction is stuck in the mempool, you (the receiver) have several options:
- creating a CPFP
- waiting while periodically rebroadcasting the signed transaction
- paying a miner to include your transaction in the block he's working on (sometimes there are miners who do this for free to)
- asking the sender to create a RBF transaction
- asking the sender to double spend the unspend outputs used in the stuck transaction to create a new transaction with a higher fee