Okay, so imagine you and your friends are playing outside and you all want to do different things. One friend wants to play basketball, another wants to play tag, and someone else wants to draw with chalk on the ground. You can all still play together but you need to figure out how to take turns and switch between activities so everyone gets a chance to do what they want.
In a computer program, the different things that need to happen are called "threads". Sometimes there might be many different threads that all have to run at the same time, but the computer can only do one thing at a time. So, just like with your friends playing outside, the program needs a way to switch between the different threads and make sure that everything gets done.
That's where GNU Portable Threads (or Pthreads for short) come in. They are a way for a computer program to manage multiple threads and make sure they all get a chance to run. It's like a conductor who helps a symphony orchestra, making sure that each musician plays their part correctly and at the right time, so that the whole piece of music sounds beautiful.
Pthreads are a set of tools that help programmers create and manage threads in their programs. They let the program decide which threads should run, when they should run, and for how long. They also provide a way for threads to communicate and share information, just like how you and your friends might shout to each other across the yard to coordinate your games.
So, to sum it up, GNU Portable Threads (Pthreads) are like tools that help programs manage multiple different things happening at the same time (threads) and make sure everything gets done. They let the program switch between the threads, communicate between the threads and make sure nothing gets left out!