This is a quick-start tutorial for the vi text editor which is available on most Unix or Unix-like systems, including Linux, macOS, Solaris, HP-UX, AIX, FreeBSD/OpenBSD/NetBSD, and Windows, and on some niche OSes too. vi, or a variant of it (e.g. vim/elvis/nvi, etc.) is one of the few text editors which is almost guaranteed to be present (or can be installed) on all of these systems.
So it's useful to have basic knowledge of its use, since it is widely applicable.
Although the vi variants have somewhat different command sets, they all share a common subset (consisting of the most commonly used operations), and a common editing model. This tutorial covers some of that subset, enough for a beginner to get started using vi to perform day-to-day text editing tasks, without getting lost in arcane command syntax.