Okay kiddo, let's talk about security interests. Imagine you have a really cool toy, and your friend wants to borrow it. But, you don't want to give it to them for free because you're worried they might forget to give it back. So, you make a deal where your friend promises to give you a cookie in exchange for borrowing your toy. That way, if they don't give your toy back, you still get something yummy in return.
Well, adults do the same thing with things that are worth a lot of money, like cars or houses. When someone borrows money to buy something expensive like a car, they might give the lender a security interest. That just means that if they don't pay back the money they borrowed, the lender has the right to take the car as payment instead.
It's like a grown-up version of trading toys for cookies. By giving the lender a security interest, the person who borrowed the money is saying "hey, if I can't pay you back, you can have this thing instead." This way, the lender is more likely to give the person the loan in the first place, because they're protected in case anything goes wrong.