Okay, kiddo. So, there are two words that people use when talking about things that you can get for free: gratis and libre. Now, even though both words mean you don't have to pay for something, they actually mean slightly different things.
When people use the word "gratis," they're usually talking about something that you can just download or have without spending any money at all. This could be a free game that you download on your tablet or a free song that you listen to on the internet. Basically, anything that you don't have to pay for is gratis.
On the other hand, when people use the word "libre," they're talking about something that's not just free to download, but also free to use, change, or share however you want. For example, if you wanted to write a story and you used a libre writing program, you'd be able to change the program to make it better for you or share it with other people who might like to use it too.
So think of it this way: if something is gratis, you can have it for free, but you might not be able to do what you want with it. But if something is libre, you can have it for free and you can also do whatever you want with it, like change it or share it with other people.