Okay kiddo, let me explain what a mechanic's lien is. Imagine you have a toy that needs fixing, let's say it's a broken car. You take it to a mechanic and he fixes your car. But he wants to get paid for his hard work, right? What if you don't have enough money to pay him?
Well, the mechanic can put a mechanic's lien on your car. That means that he can keep your car until you pay him for his work. He has a right to get paid for the work he did fixing your car.
Now let's say you can't pay him and you want to sell your car to someone else. You can't do that because the mechanic's lien is still there. The new owner can't take your car until you pay the mechanic what you owe him.
So, a mechanic's lien is a way for mechanics to make sure they get paid for their work. It's a legal way for them to keep your car until you pay them what you owe.