Database formulas

Hello,

I have this problem that is bugging me because I can't figure out how it's done.
I know it is something simple, but for some reason I cannot find the answer on google. It's probably because english is not my native language, so I don't really know what to google. I tried and I tried to google anything related to this, but it did not answer my question.

So the problem is very easy: I have a table, a database, for which I need to count the number of employers, based on a criteria.
This would be very easily done with a DAVERAGE.
However, I need to display the average by city.

I have this already solved in my file, I just can't figure out how it was done and I can't replicate it.
Please see the screenshot.
I understand the DAVERAGE formula; I know that I have to press CTRL+SHIFT+ENTER, cause it's an array formula;
The 3 cells on column C are the cities from the table and the cell marked with blue on column A is the column name of the cities.
Do I put the cities there manually (copy paste the entire column, remove duplicates?) or how did they get there?
I know it has something to do with having the column name of the city there as criteria, I just can't figure out how.

A4:H25 is the database, A4 is the first column name.

excel2.PNGexcel1.PNG

So I can you help? I know it's something really stupid.

Thank you,
Alina