[Solved] Improve year&month summary method

[Cobbles_Classics]

Hello all.
I am using calc for my accounts in conjunction with a MTD (Making TaxDigital) program.
The program, requires the use of XLS format so I have to work with that.

I have a complex spreadsheet for my monthly accounts.
Rather, than one sheet for sales and another for purchases, I have shown an example of one method that i use (top section A1-S7

I would like to simplify this, and use a drop down menu (see below example) i A10 - M14 with B11-B14 being the key.
Ideally, I would be able to use the drop down to determine whether it is a sale, or a purchase, and it would then calculate the total, for that particular month and year.
You can see how I use it currently in the top example, but I feel, it's something I could improve, if I knew the method or direction, I should be looking within, to solve.

Any polite advice, would be welcome,
Thank you.

Edit: Changed subject, was Trying to find a more effective method  Make your post understandable by others  -- MrProgrammer, forum moderator

[MrProgrammer]

Ideally, I would be able to use the drop down to determine whether it is a sale, or a purchase, and it would then calculate the total, for that particular month and year.

Calc Guide Chapter 8 - Using a Pivot Table   (formerly called Data Pilot)

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[Cobbles_Classics]

Thank you Mr Programmer - I will have a read.

[Cobbles_Classics]

Any other suggestions, or thoughts, that may overcome the inability for a auto updating spreadsheet, linking to MTD software, using pivot table?

The example i added, shows how it used currently, and I felt that a more simple solution, would be possible?

[Cobbles_Classics]

Hello again.
I discovered an easier way, without using a pivot table - thank you to Mr Programmer for pointing me in the right direction.