Well, a gnutella crawler is like a special little robot that goes around on the internet looking for files to share with others. It goes from computer to computer, asking if they have any files that people might be interested in, like music or movies.
But wait, how does it know where to go or what files to look for? Well, it uses something called metadata, which is like a little tag that describes what a file is. So if someone wanted to find all the songs by their favorite artist, they could tell the gnutella crawler to search for files with that artist's name in the metadata.
Once the gnutella crawler finds some files, it adds them to a big list that other people can access when they're looking for things to download. And when someone else finds something they like on the list, they can download it from the person who originally shared it.
So basically, a gnutella crawler is a little robot that helps people share files more easily on the internet. Cool, huh?