Shell Programming: find Command
When you have lots of files, manually digging through directories level by level becomes very inefficient. The value of find is that it can locate files by name, type, size, time, permissions, and other criteria -- and then chain further batch operations.
This material pairs well with daily tasks like organizing projects, searching logs, and cleaning build artifacts. Once you're comfortable with it, find goes from being "that long command" to a fundamental tool for finding things on servers.