Have you looked in the Product Documentation? Entering "dashboard" in the Help Search gets you a lot of hits. The first one, the "Ariba Strategic Sourcing and Contract Management Basics" Guide has an entire chapter on Working with Dashboards.
As for mobile, you can access the Ariba Solutions via mobile but the dashboards are not optimized for mobile. You will just see the dashboard in the mobile browser as any other page in the solutions. We have mobile applications in our roadmap for future development.
David Morel