Start here. This is the direct spoken answer to practice first.
Overview
Starters select a coherent capability classpath; dependency management aligns versions; auto-configuration reacts at runtime.
A Spring Boot starter is a convenient dependency descriptor for a capability such as web, validation, or data access. It brings a curated set of libraries so the application does not select every transitive dependency manually. Boot's dependency management supplies compatible versions for supported libraries. A starter does not itself create beans; the resulting classpath can make Boot auto-configuration conditions match when the application starts.