Once you start Power View, the interface you will see will be a bit different depending on whether you are using Power View through SharePoint or Excel.

Power View through SharePoint looks like this:

Power View in SharePoint

Power View through Excel looks like this:

Power View in Excel 2013

Note that in SharePoint there is a View Area, while in Excel there isn't one. The biggest difference is with the ribbons. In Excel, there are three ribbons that are used exclusively by Power View. The Power View ribbon is always visible, as shown in the following screenshot:

The Power View ribbon in Excel 2013

The Design ribbon, as shown in the following screenshot, is visible when a visualization is selected:

The Design ribbon in Excel 2013

The Layout ribbon, as shown in the screenshot, is visible when a chart is selected:

The Layout ribbon in Excel 2013

In SharePoint, you have the Home ribbon, which is always visible, as shown in the following screenshot:

The Home ribbon in SharePoint

The Styles...