Github git

Download single file

curl -O wget https://raw.githubusercontent.com/user/project/branch/filename

Github push/pull with SSH key

You'll need to change the github URL you are using.

git clone https://github.com/<Username>/<Project>   # !!bad!!

git clone git@github.com:<Username>/<Project>       # good
git clone github.com:<username>/<project>           # also good (must specify user in ~/.ssh/config)

You can quickly test authentication

ssh git@github.com -i ~/.ssh/github

importing existing git repo

See hosting a git http server to share with github.

You can then use that to import your project.