1. Introduction

This tutorial will guide you on how to manage large projects or include external libraries into your project using Git submodules and subtrees. You will learn the differences between submodules and subtrees, and how to use each effectively in your project.

By the end of this tutorial, you will be able to:
- Understand the concept of Git Submodules and Git Subtrees
- Create, update and delete Submodules and Subtrees
- Resolve common issues that arise when using Submodules and Subtrees

Prerequisites:
- Basic knowledge of Git
- Git installed on your local system

2. Step-by-Step Guide

2.1. Git Submodules

Git Submodules allows you to keep a Git repository as a subdirectory of another Git repository. This lets you clone another repository into your project and keep your commits separate.

2.1.1. Adding a Submodule

You can add a submodule to your repository using the git submodule add command followed by the URL of the repository. This will create a new file called .gitmodules which maps the project URL to your local subdirectory.

git submodule add https://github.com/username/repo.git

2.1.2. Cloning a Project with Submodules

When you clone a repository which contains submodules, you need to initialize these submodules using the git submodule init and then run git submodule update.

git clone https://github.com/username/repo.git
cd repo
git submodule init
git submodule update

2.2. Git Subtrees

Subtrees allow you to nest one repository inside another as a sub-directory and yet retains the ability to split the section back out into its own repository later.

2.2.1. Adding a Subtree

You can add a subtree to your repository using the git subtree add command.

git subtree add --prefix=subfolder_name https://github.com/username/repo.git master --squash

3. Code Examples

3.1. Git Submodule

Here's an example of creating a new submodule, initializing it and updating it.

# Add the submodule
git submodule add https://github.com/username/repo.git
# Initialize the submodule
git submodule init
# Update the submodule
git submodule update

3.2. Git Subtree

Here's an example of adding a new subtree to your repository.

# Add the subtree
git subtree add --prefix=subfolder_name https://github.com/username/repo.git master --squash

4. Summary

We've covered how to manage large projects or include external libraries into your project using Git submodules and subtrees. We've learned how to add, initialize, and update submodules as well as how to add subtrees.

For further learning, you can look into:
- Resolving conflicts in submodules and subtrees
- The use of git submodule status and git submodule summary

5. Practice Exercises

1. Exercise 1: Create a new Git repository and add a submodule to it.
2. Exercise 2: Clone a repository that contains submodules and initialize and update the submodules.
3. Exercise 3: Create a new Git repository and add a subtree to it.

Solutions:

1. Solution 1:
   bash git init git submodule add https://github.com/username/repo.git
2. Solution 2:
   bash git clone https://github.com/username/repo.git cd repo git submodule init git submodule update
3. Solution 3:
   bash git init git subtree add --prefix=subfolder_name https://github.com/username/repo.git master --squash

Keep practicing and exploring more commands related to git submodules and subtrees. Happy Coding!