Base Layer – The Blockchain
On average, every 10 minutes a block will be ‘mined’ and this will be the first confirmation that the transaction was successful and finalized on the blockchain. Sometimes you will get a miner who mines faster or slower than the average 10 minutes, but over time, the average is 10 minutes by way of the protocol rules.
You can see on mempool.space a graphical representation of the blockchain and an example of its mempool where transactions that have not yet been confirmed are waiting to be confirmed. There is not a centralized mempool. Each Bitcoin node has its own mempool and rules on how large it can get in megabyes. The default for most instances is 300MB, but the node operator can increase that or decrease that as they please.
Most day to day spending that you would normally do would not be a good idea to do on the base layer due to the 10 minute average transaction time. This is why there is a 2nd layer.
2nd Layer – Lightning
The lightning layer is MUCH faster. An entire transaction can settle and confirm in a fraction of a second. It can do this because the lightning layer relies on inter-connected nodes that have decided to tie up their bitcoin with each other like an abacus. The lightning layer relies on a centralized group of lightning nodes that have a connection like six degrees of separation. If your lightning wallet can find a connection to the recipients lightning wallet through a number of lightning nodes, it’s just like an abacus where some Bitcoin is moved from one side of the abacus to another all along the route until it gets to the destination. Each routing node takes a small amount of Bitcoin as a transaction fee for using their node. This equates to a VERY SMALL fraction of Bitcoin in the realm of 0.00000001 or even less than that.