Okay, so imagine you have a lot of important papers and you want to keep them organized. One way to do this is by putting them all into a special kind of folder that is labeled so you know what's inside. This is kind of like a computer file.
Now, sometimes when you want to share your papers with someone else, you might make a copy and give it to them. But you have to make sure they can read it, right? That's where "file formats" come in.
A "file format" is like a special language that your computer uses to know how to read and understand your papers (or files). Just like how you and your friends might use different languages to talk to each other, different computers and programs use different file formats to understand and read files.
One of these file formats is called "PLS". It's used by a music program called Winamp to read and play certain kinds of music files. So if you have a music file you want to play in Winamp, you need to make sure it's in the right file format (in this case, .PLS). Otherwise, Winamp won't know how to play it and you won't be able to hear your music!
So, to sum up: a "file format" is like a special language that your computer uses to understand and read your files. The PLS file format is used by the Winamp music program to read and play certain types of music files.