Git Survival Guide
This guide is a good starting point and reference for Git and related services.
Background
Git is a distributed version control system, originally developed by Linus Torvalds and others to develop the Linux kernel.
Git usually pairs with an online service like Github and Gitlab which maintains a highly distributed data system. Distributed means that is highly available, resilient, and secure. This makes git + Github/Gitlab ideal for secure code and data storage. Git is the industry standard for modern software (and data) revision control.
Note
The name git comes from old British English and signifies an annoying or unpleasant person. To understand the full meaning of the word git, see https://en.wikipedia.org/wiki/Git_(slang) .