First, head to https://my.otus.com, and click the Microsoft button.
Enter your Microsoft email address, then click Next.
Enter your password, and click Sign In.
The first time you log in, you'll have to allow Otus to access certain data stored in Microsoft. Click Yes to continue.
You're now logged into Otus with your Microsoft SSO! If you're already logged into Microsoft when you attempt this, you'll skip the email and password steps, and just have to click on the email you wish to sign in with.