MS SQL Tips has a nice primer on PowerPivot with Excel 2013. There is chapter in my upcoming book, Building Dashboards with Dynamics GP 2013 and Excel 2013 on PowerPivot. You’re going to love it.
PowerPivot with Excel 2013
Excel & OfficeGP 2013
Archived post from 2013. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.