The Questions panel contains all the questions that are available in the currently selected datasets. Colors on the left side of the questions display the compatibility. Read more in Working with multiple datasets.
Tabs
Use tabs to switch between Objects&KPIs, Questions / Splits and the list of User Defined Filters (for details about this section see User Defined Filters (UDF)).
Left click will expand or collapse the whole section of questions. Left clicking on menu or right clicking on section name will open the Section context menu.