GoogleSign-In is a plugin for SuiteCRM
This plugin provides log in functionality using existing google credential rather than creating separate login credential for CRM.
Before moving further, first we need to configure a project in Google Developer console. This is a one time activity. Once you register your project, you'll get Client ID and Client Secret and those details need to be saved in CRM.
Once you saved those details, then you'll get to see the Sign in With Google button on login screen. Before logging in using google credentials, kindly make sure that your google email address is stored as the CRM user's primary email address.