I just asked AI to ELI5.

Imagine you have a piggy bank full of coins. Each coin represents a UTXO. When you want to spend Bitcoin, you take some coins out of your piggy bank and send them to the person you are paying.

The more coins you take out, the heavier your transaction will be. Miners charge fees to process transactions, so the heavier your transaction is, the higher the fee will be.

You can reduce the fee by combining multiple coins into a single coin before you send it. This is like taking a bunch of small coins out of your piggy bank and exchanging them for a single large coin.

You can also reduce the fee by waiting for a time when there is less demand for block space. This is like waiting until there is less traffic on the road before you drive to your destination.

Here is a simplified analogy for a 5-year-old:

Imagine you are standing in a line at the store with a bag of candy. Each piece of candy represents a UTXO. When you want to buy something, you hand the cashier some candy from your bag.

The cashier needs to count your candy to make sure you have enough to pay for the item. This takes time, so the cashier charges a fee for each piece of candy that they have to count.

You can reduce the fee by putting all of your candy into a single container before you go to the store. This way, the cashier only has to count the candy once.

You can also reduce the fee by going to the store at a time when there is less traffic. This way, the cashier has more time to count your candy.

I hope this helps!