The purpose is always the same: To learn. It's how you learn and what your learn for that are different. A tutorial is for getting exposed to something. A guide is for a very specific purpose in something you're already familiar with. An explanation is for a deeper understanding and references are for not relying on memory. They all refer to different things that ultimately falls under the same concept (and intersect with each other). If you're building a system, you should have all of them otherwise, the documentation is lacking.
