To be able to use chisubmit, you will need to initialize a directory (typically, but not always, a directory containing a Git repository for the course you are taking) so that you can run chisubmit commands in that directory (and, in fact, anywhere in that directory tree).
In that directory, run the following:
When prompted for your “chisubmit username” and “chisubmit password”, just use your CNetID and password. Once you have entered your username and password, you will be shown a list of courses you belong to in chisubmit. If the course you are using chisubmit in does not appear in that list, your registration information may not have been added to chisubmit.
After chisubmit init runs successfully, you will be able to run chisubmit commands from inside that directory.