git clone <url>
Most probably, your URL is not valid.
If it is a http/https URL, you can quickly check, by hammering the URL into a browser. If that does not display anything at all, you know that the URL is invalid.
I assume you are speaking of a remote repository. The URLs should look somewhat like these:
https://github.com/user/repo2.git if you're using HTTPS [email protected]:user/repo2.git if you're using SSH