Login screen is the first one you see when you launch Glue. In addition to Login it contains a “Forgot Password” link that you can use for resetting the password for your Glue account.
There are three ways to Login to Glue:
Your email & password
Creating a Glue account for Login is recommended. You can create yourself a Glue account in the process of being invited as a member to a Glue Team, or in the process of creating a Free Tier Team in Glue. You can create a Glue Free Tier Team on Glue website in Get started with Glue.
Login with your Google credentials
You can also use your Google credentials for Login to Glue
Device codeDevice code option is there mainly to ease the Login for standalone VR device users. Obviously it can be used on other platforms too. How it works is that if you are Logged in to Glue Web with your desktop computer, adding the Device code there will Log you in to the Glue application too.