Quick Definition Lookup shows you where and how your project symbols (tags, classes, methods/functions, fields, etc) are defined.
Definitions are shown in the Documentation popup or in the Documentation tool window.
View the definition of a symbol at caret
Select a symbol and press Ctrl+Shift+I or choose.
Open the definition in the Documentation tool window
In the hover mode, move your mouse pointer within the tooltip and click in the upper-right corner.
Jump to the definition of the symbol
When in the hover mode, just click the link into which the symbol has turned.
To open the source code of the definition for editing and close the quick definition lookup window, click on the toolbar or press F4.
To open the definition without closing the quick definition lookup window, click or press Ctrl+Enter.
Toolbar of the quick definition lookup
Use the icons on the toolbar of the popup to navigate to the source code of the definition and view its usages.