Actually pivot table does not support group dates by the day of weeks. However, we can add a helper column about day of week in the source data, and then group dates by the helper field in your pivot table. Please do as follows:

1. Insert a blank column in the source data, type Day of Week as column name, next type the formula =TEXT(A2,"ddd") in the first cell of the helper column, and finally drag AutoFill Handle down to fill the whole column. See screenshot:

2. Select the source data, and click Insert > PivotTable.

3. In the Create PivotTable dialog box, select a destination range to place the pivot table, and click the OK button.

4. In the PivotTable Fields pane, please drag and drop the Day of Week field to the Rows section, and drag and drop the Sales field to the Values section. See screenshot:

And now you will see the dates are grouped by the day of weeks in the new created pivot table automatically. See screenshot above.

Note: If you want to group the dates by month and day of week together, please go ahead to modify the pivot table:

(1) In the PivotTable Fields pane, drag and drop the Date field to the top of Rows section.

(2) In the pivot table, right click any date in the Row Labels column, and select Group in the context menu. Then in the Grouping dialog box, click to highlight Months only in the By list box, and click the OK button. See screenshot:

Now you will see the dates are grouped by both months and day of weeks in the new created pivot table. See screenshot:

If you have Kutools for Excel installed, you can apply its PivotTable Special Time Grouping tool to quickly create a pivot table and group the pivot table data by the day of week automatically.

1. Select the data you will create a pivot table based on, and click Kutools Plus > Pivot Table > PivotTable Special Time Grouping.

2. In the PivotTable Special Time Grouping dialog, do as follows:
(1) Tick the Day of week option in the Group By list box;
(2) Specify the date column from which you will get the day of week data;
(3) Specify the location that you will place the new pivot table.

3. Click the Ok button. Then a pivot table is created with a column of day of weeks.

4. Go ahead to complete the building of the pivot table: drag the Sales field and drop it in the Values section.

Then you will see the sales data is added into the pivot table, and grouped by the day of week. See screenshot:

Easily groups cells and calculate by values in another column in Excel

With Kutools for Excel’s Advanced Combine Rows feature, you can quick group all cells of one column based on values in another column, or calculate (sum, count, average, max, etc.) these cells by the values in another column at ease!