This is a beginner level android project.
Firstly you need to fork(using the fork button in the right up corner) this project and then clone it on your local machine and then open your Android Studio and then open the express directory in your Android Studio and then start building this project(it will take time depending on your net connection speed).
Make sure you have git installed on your machine before proceeding further.
If you do not have git installed then follow this:
For Linux Machine you can go here
For Windows Machine you can go here
For cloning you can use a terminal if you are on linux and terminal on windows just type
git clone https://github.com/YourGitUserID/Droid_project/
Alternative of cloning you can simply download the repo in zip format.
For this you can read this