Quick Definition Lookup shows you where and how your project symbols (tags, classes, methods/functions, fields, etc) are defined.
View the definition of a symbol at caret
Select a symbol and press Ctrl+Shift+I or choose.
Jump to the definition of a symbol
Click the icon in the top-right corner to open the definition in the Find tool window. To open the source code of the definition for editing and close the popup, click the icon F4. To open the definition without closing the popup, click the Ctrl+Enter.