Git: Permission denied (publickey)

Hello! I have a question about Git. I’m trying to setup Git on the WPMU hosting and I can’t seem to get it to work.

I’m getting the following message whenever I try to “git push”:

git@github.com: Permission denied (publickey).

fatal: Could not read from remote repository.

I’ve setup a repository on Github and added a SSH user on the WPMU Hosting with a public key. Through SSH, I’ve done “git init” and “git remote add ….” etc.

Is there anyone who can tell me the steps I have to take? I know I’m doing something wrong, but I don’t know what. I can’t find any documentation so I thought I’d ask here.