GEM uses SSO (Single Sign-On) to access Salesforce. Your Microsoft 365 credentials are connected to Salesforce.
The easiest way to access Salesforce is by using this link:
https://gemission.lightning.force.com/
Alternatively, you may be presented with a login screen like this one, select "Use Custom Domain"
Enter "gemission" in the prompt for a Custom Domain.
If you are presented with a login screen like this one, then select "Login with Microsoft 365".
If you are already logged in with your GEM Microsoft 365 account, you will be automatically logged into Salesforce. If not, then complete the login process with your GEM Microsoft 365 account.