Abhidhamma Pitaka is a collection of Buddhist scriptures that try to explain how the mind works and how it relates to the world around us in a very detailed way. These scriptures are like very big puzzles that have lots of pieces about how things work together.
Think of your mind like a computer that works all the time. It takes in information from your eyes, ears, nose, tongue, body, and mind, and then it sorts it all out and helps you understand what is happening around you. Abhidhamma Pitaka tries to explain how all these puzzle pieces fit together, so we can understand how our mind works and how we can develop it to become a wiser and kinder person.
The puzzles in Abhidhamma Pitaka can be quite tricky, so monks and scholars spend many years studying them to understand them fully. But just like you need to learn how to read before you can understand a book, you need to learn about Buddhism to understand Abhidhamma Pitaka.