How do I use tableau Mobile with Active directory to log into tableau dashboards published. How does this authentication method work or do I need to use local authentication methods for users in-order for them to access the dashboards.

Active Directory authentication is simply noting that authentication is passed on to AD. Mobile user still able to type in their AD username and password and should pass get authenticated and valid session for access. If you want automatic login, then you may need a VPN profile configuration to pass on an AD credential