@arina98
Click anywhere in the data table.
On the Insert tab of the ribbon, click Pivot Table.
Specify where you want it, then click OK.
Drag the date field to the Rows area.
Drag the field that you want the average of to the Values area.
Click on the field in the Values area and select 'Value Field Settings'.
Select Average as function, then click OK.
Right-click any of the dates in the pivot table.
Select Group...
You can specify whether you want to group by days or months.
