To log in to portal.office.com, start by opening a web browser and entering the URL: portal.office.com. This will take you to the Microsoft Office 365 login page. Enter your email address associated with your Microsoft account, then click Next. Input your password and press Sign In. If your account uses two-factor authentication, you may need to verify your identity via a code sent to your phone or email. Once logged in, you will gain access to Office 365 apps like Outlook, Word, Excel, and Teams. Make sure to sign out after use if on a shared device.