The Finances panel provides a place for you to display roll-up information of child components - projects and sub-portfolios. You can also display to-date information based on the roll-up date ranges (earliest start to latest target of all child projects or portfolios).
You configure the Finances tab exactly like you configure the Details tab - the difference is that a set of finance fields/group headers has been placed on the Portfolio Finances page by default. Just like with the Details tab, you can add/remove fields, configure whether fields should be visible/editable when creating a new portfolio, change field display names, and so on. Any Available Fields-level field restrictions you configure will be in effect if you use the fields on the Finances tab; these restrictions, if any, would be displayed in the read-only Restrictions section when you select a field on the Finances tab.
See Designing the Details Page for information.