When you are working within a single portfolio, you have access to a collection of reports or "views." These views may feature some ability to customize the output, such as using a particular date range, and allow you to print. But the holdings displayed in a view are restricted to the holdings in the current portfolio. Views are intended to be quick looks at a portfolio's key fundamentals.
The Advanced Reports, available from the top level menu on the right side of the page, allow you to include holdings from two or more portfolios in a consolidated display. In many cases, the information in the report may be identical to a corresponding view, but there are some additional reports available as well as some additional display criteria that you can select.
The Performance Report is one example of an Advanced Report. It calculates a benchmarked performance figure for an entire portfolio or group of portfolios, comparing the cash flows of your selected portfolios to a similar set of hypothetical cash flows in a index (as represented by a low-cost index fund).
Once you understand how Views and Reports work, you can explore them and find the information that provides the best intelligence for your portfolio management needs.