In this video we explore how to measure the efficiency of algorithms by comparing their complexity and cost. We differentiate between problems, algorithms, and programs, and discuss how to measure complexity theoretically or experimentally. We examine two dimensions associated with problems: size and instances. This is illustrated through an animation comparing Insertion Sort and Selection Sort, showing how they perform differently based on the input array. The video highlights three main measurements of algorithm efficiency: time cost (related to execution speed), space cost (related to memory usage), and energy cost (related to power consumption).