To log in to your account, click the gray "Log in" button in the upper right corner of the website:
If you created your Boundless account using your Facebook credentials, click the Facebook button. This will use your Facebook login info to get into Boundless.
If you created your Boundless account with your Google Plus credentials, then click that button, and log in with your Google credentials.
If you signed up using your email address, fill in your email and password to access your account.