Here is a simplified explanation of what I am trying to do:

I have created a table, where Column A contains some data, in Column B user
selects a category (A, B, C,...) and in Column C user sets a priority (1, 2
or 3).

Now, I am trying to count how many rows we have, where something has been
written in Column A, Column B has been set to A and Column C has been set to
1.

I have tried this as follows: COUNTIF(Column A; AND(Column B = A; Column C =
1), but it doesn't work. Any ideas?