How git clone actually works

Question

I have a repository on Github with 2 branches: master and develop.

When I clone the repository and run $ git branch it shows only the master branch.
If I run $ git branch -a I can see all the remote branches.

Now, if I do a $ git checkout develop, I get the message:

Branch develop set up to track remote branch develop from origin.
Switched to a new branch 'develop'

What actually happened? Were the commits from the remote develop branch fetched when I ran $ git clone remote-url, or when I ran: $ git checkout develop, or neither?

Have I to do a $ git pull origin develop after checking out develop, or it's already done?

Please help me understand how clone works when there are multiple branches on remote.

Answer 1

To put it simply, git clone repository-url does the following things, in order:

1. Creates a new empty repository.

   git init
   

2. Creates a remote called "origin" and sets it to the given url.

   git remote add origin repository-url
   

3. Fetches all commits and remote branches from the remote called "origin".

   git fetch --all
   

4. Creates a local branch "master" to track the remote branch "origin/master".

   git checkout --track origin/master
   

An interesting point is that a fork (in GitHub or Bitbucket) is just a server side clone.