The tools you need will depend on which components you are working on.
Make a copy of Fork a Github Repo
Graph Genome Browser Consortium GitHub
Github Code Repos - Component Source Code
Basic command to clone a repo
git clone git@github.com:graph-genome/Schematize.git
Work locally on your own version of the source code
Modify the files with your favorite text editor or IDE
Commit your changes to your version of the repo
Generate a Pull Request to share your changes with the team
Read this excellent tutorial on how to Create a Pull Request