This is a quick overview of the Windows 8 table app for approvals that can be used with Dynamics AX 2012. This is one way to allow a mobile workforce respond to notifications from workflow.
There are other ways for employees to get access to these notifications. For example in the AX Windows Client, on the role center, via email. Email approval can be done via any email client. This was a feature introduced around the Dynamics AX 2012 R2 timeframe.