Animating with keyframes in Anime.js allows you to move an element through a series of defined states, creating smooth and complex transitions. The keyframes array is where you specify each step of the animation. Each object inside the array represents a new state for your target element, defining which properties to animate, their values, and optionally, the duration for that particular step.

For example, in the code above, the circle starts at its initial position and color, then moves horizontally to the right while changing to red, drops down while turning yellow, slides back left and becomes green, and finally returns to its starting point and blue color. Each step in the keyframes array describes both the visual style and position for that segment of the animation.

Anime.js automatically interpolates between the values defined in each keyframe, ensuring transitions are smooth and continuous. You can animate multiple properties at once within each keyframe, and even set different durations for each step. This makes keyframes a powerful tool for crafting engaging, multi-stage animations without complex code.