Perhaps the simplest model to think about is to look at what happens when you pay with banknotes in a store.

Suppose you have $20 and $10 banknotes and pay for an item that costs $22.

You give two banknotes $20 and $10, the cashier takes $22 and you get $8 back.

Bitcoin mimics this process. We just call these banknotes "outputs" and they can hold arbitrary value. So in this case, a transaction would
1. use two outputs with $20 and $10 (in btc of course) and
2. create two new outputs. One holding $22 whose owner was the cashier and one holding $8 with you as the owner

We call used outputs "inputs". It effectively splits some of the existing piles of coins (inputs aka old outputs) into new piles of coins (new outputs) and sets the owners as defined. Just like in a store.