2 methods can be used here.
1. User Account Disabled option on Employees section can be marked to prevent the user to login to the system.
2. By entering the dates that you want to prevent the users to login to the system to the inactive date section on status section, the users will not be able to login. This method can usually be used for employees who are on leave. Inactive or disabled users can be viewed separately by clicking the icons above the Employee section.