1. To split off (from a larger group) into smaller groups or discrete parts. The desk separates into six pieces that can be easily fit back together. The class separated into groups of five while going through the museum exhibit.

2. To divide a group of people or things into smaller, discrete subgroups. In this usage, a noun or pronoun is used between "separate" and "into." Please go through that huge stack of books and separate them into three piles—ones you want to keep, ones you want to sell, and ones you don't mind giving away. They separated all the students into different groups based on their age.