When you only see an option to sign out of the Don Johnston Tools website then you are logged in with a Student Account. Student accounts only have access to the Don Johnston Tools website the first time they login to see the tutorial and install the extension if it is not installed.

Student Account first time Logging in to website:

Student Account logged into tools website after the tool is installed.

Student Account logging into a Don Johnston tool Website they have not been invited to.

You would need to contact your schools licensed web admin for the Don Johnston tool and ask them to invite you as an educator to the school/organizations license.