Lesson 2: Git vs GitHub: Repositories, Commits, Branches

Before you start

This course follows Microsoft's Study guide for Exam GH-900: GitHub Foundations. The guide belongs to Microsoft, is free on Microsoft Learn, and is not reproduced here. This course is independent: GitHub and Microsoft do not endorse it, and it cannot promise that you will pass.

This level covers two bullets from the domain Understand Git and GitHub basics (25–30%):

• Explain the difference between Git and GitHub
• Identify key Git concepts such as repositories, commits, and branches

Step 1: Separate Git from GitHub

In Level 1 you learned what version control does. Now meet the two names the exam expects you to keep apart.

GitHub's documentation calls Git "the most popular distributed version control system". It says GitHub "hosts Git repositories and provides developers with tools to ship better code."

Analogy: Git is the camera that takes the photos. GitHub is the online album where you store and share them, and where others can comment.

Distributed means every copy of a repository on every computer has the complete history. You can commit on a plane with no connection and share your work later.

Do this: Say the difference out loud in one sentence: "Git is the tool that tracks changes. GitHub is the platform that hosts Git repositories online."

Step 2: Learn the three key concepts

1. Repository (repo): GitHub Docs defines this as "the entire collection of files and folders associated with a project, along with each file's revision history." It is the project folder plus its memory.
2. Commit: a saved snapshot of the project at one moment, with a message that describes the change. Commits link together to form the project's history.
3. Branch: an independent line of development. You can work on a branch without touching the main line. New GitHub repositories use main as the default branch.

Analogy: The repository is a notebook. Each commit is a dated page. A branch is a sticky-note tab where you draft ideas without changing the clean copy.

Step 3: Create a repository with git init

Install Git from git-scm.com, open a terminal and follow these steps:

1. Make a folder and move into it:

   mkdir my-first-repo
   cd my-first-repo
   

2. Turn the folder into a Git repository:

   git init
   

   Git creates a hidden .git folder, which is where the history is stored. The folder is now a repository.
3. Tell Git who you are (once per computer). Git attaches this name and email to every commit:

   git config --global user.name "Your Name"
   git config --global user.email "you@example.com"
   

Note: If you haven't set a default branch name, plain Git may call the first branch master. Run git config --global init.defaultBranch main to match GitHub.

Step 4: Save a snapshot with git add and git commit

Saving a change takes two steps: stage it, then commit it.

1. Create a file, for example README.md, containing one line of text.
2. Stage it, which means choosing what goes into the next snapshot:

   git add README.md
   

   (git add . stages every changed file in the folder.)
3. Record the snapshot with a clear message:

   git commit -m "Add README"
   

4. Check your work: git status shows what is staged, and git log lists your commits.

Analogy: git add puts items into the box. git commit seals and labels the box.

Step 5: Work on a branch with git branch and git switch

1. Create a new branch:

   git branch add-intro
   

   This only creates the branch. You are still on main.
2. Move onto it:

   git switch add-intro
   

3. Shortcut that creates the branch and switches to it in one step:

   git switch -c add-intro
   

4. Run git branch with no name to list branches. The current one is marked with *.
5. Edit README.md, then run git add and git commit again. The new commit exists only on add-intro. main is unchanged.
6. Return with git switch main.

Note: Older guides, including some GitHub Docs pages, use git checkout <branch> to switch. git switch was added in Git 2.23 (2019) for exactly this job.

Command summary

What the exam asks about this

GH-900 questions on this topic are usually short definitions or scenarios. Expect to:

• Choose which statement describes Git (a local, distributed tool) and which describes GitHub (a cloud hosting and collaboration platform).
• Match a description to the right term: "a snapshot of changes" is a commit, "a separate line of development" is a branch, and "project files plus their full history" is a repository.
• Spot the false claim. Git does not need GitHub or an internet connection to record history.
• Put steps in order: git init → git add → git commit.

Key takeaways

• Git is a distributed version control system that runs on your computer. GitHub is a cloud platform that hosts Git repositories and adds collaboration tools.
• A repository holds a project's files and their complete revision history.
• A commit is a snapshot with a message. Saving one takes two steps: git add, then git commit.
• A branch is an independent line of development. git branch creates one, and git switch moves to it.
• git switch -c <name> creates a branch and switches to it in one step.