It makes sense to create groups in Active Directory for SharePoint authentication, rather than adding users to SharePoint individually, but you already knew that. If you are trying this by yourself for the first time, you might make the same mistake that I did. I right clicked on "Users" and created groups, but SharePoint ignored them, and all the member users could not login to SharePoint. I needed to create groups elsewhere...
Do not add Active Directory groups from "Users" for SharePoint
Note: In the examples below, [home.local] is the name of my test domain
SharePoint HATES:
Active Directory Users and Computers / [home.local] / Users / <right click> / New / Group
Group Name: mygroup1
Group scope: Global
Group type: Security
Creates
"CN=mygroup1,CN=Users,DC=home,DC=local"
Add mygroup1 as member of a SharePoint site
Users in mygroup1 cannot log into SharePoint "Error: Access Denied"
SharePoint LIKES:
Active Directory Users and Computers / [home.local] / <right click> / New / Group
Group Name: mygroup2
Group scope: Global
Group type: Security
Creates
"CN=mygroup2,DC=home,DC=local"
Add mygroup2 as member of a SharePoint site
Users in mygroup2 can log into SharePoint
Conclusion:
Add groups by right clicking on [home.local], NOT on "Users"