Okay kiddo, Liens are like stickers that grownups put on their things to make sure they get paid. Imagine your dad owns a big toy store and he needs to borrow some toys from his friend. But to make sure his friend gives the toys back, he needs to put a sticker on them that says "This toy belongs to Dad's store until he pays his friend back."
Now, imagine a grownup buys a car but they don't have enough money to pay for it right away. The person who sold the car can put a sticker on it, which is called a lien, that says "This car belongs to me until you pay me back".
This means that if the grownup wants to sell the car or get rid of it, they have to pay the person who put the sticker on it first. It's like a promise to pay back the person they owe money to before they can fully own the thing they bought.
So liens are basically a way to make sure that people who lend money or sell things get paid back or compensated for what they've sold.