You can activate and deactivate users in the organization by navigating to your organization's users list by clicking on your profile icon and selecting Organization Users.
Select the menu icon next to the user, select Activate User to activate a deactivated user, or Deactivate User to deactivate an activated user.
A deactivated user would no longer have access to your organization. You can reactivate the user's account if you want the user to regain access.