It's not possible to make your own account, or to sign up for Schoolrunner independently. Schoolrunner works with schools and districts, so you can only access Schoolrunner if you're a current partner.
If you're a teacher and are at a school that currently uses Schoolrunner, please enter your work email address in the "Forgot your password?" form on the login page (you may have to first click the "Sign in with email or username" link). If your address is not recognized, contact your Schoolrunner lead to ensure they have set up your account properly. More here.
If you're a parent or teacher at a school that already uses Schoolrunner, first check with the school to ensure they use the Schoolrunner portal. If they don't, it's not possible to log in. If they do use the portal, credentials will be supplied from your teacher or school. More here.