To log in, you must use your username and your password.
Some users' username is their email, whereas some user' username is a separate username. The login page for Sprout Studio says "Username or Email, " but that only says so because those users whose username is their email will not know what their username is.
Be sure to log in using your proper username. If you never created a username, your username is probably your email.
If you can't remember your username and your email doesn't work, click the "Forgot Password" button, type in your email and your password will be reset.
To change (or check) your username, go to Settings > Account & Branding > Users and click "Edit" on your user account.