This document introduces data structures and their classifications. It defines data structure as a structured way of organizing data in a computer so it can be used efficiently. Data structures are classified as simple, linear, and non-linear. Linear structures like arrays, stacks, and queues store elements in a sequence while non-linear structures like trees and graphs have non-sequential relationships. The document discusses common operations on each type and provides examples of different data structures like linked lists, binary trees, and graphs. It concludes by noting data structures should be selected based on the nature of the data and requirements of operations.