This might be the first time you use github.

1 - Press the green button "Clone or download"

2 - Copy the url

3 - Open Sourcetree, select File->clone a repository

4 - Enter the url and where you want to save the game on your pc

Open unity and press "Open", select the folder where you put the game.

Do stuff!

Double click on a C# file, it will open Visual Studio or a code editor of your choice.

1 - Do a change, anything!

2 - Open SourceTree, select the "File Status" tab

3 - See all the changes you've done, file by file

4 - Stage the changes you want to upload

5 - Enter a relevent message in the message box of what you've done

6 - Press commit and tick the "push" box

7 - The changes you've done are now online!

You should try to keep up to date as best as you can

To do so, simply press "pull" in SourceTree, this will fetch the latest changes.