Jogamel, I have the same four blank squares. If you follow the two instructions given by the first and last letters of the extra words, the one half of the grid literally sits on top of the other, with the blanks (holes) replaced by the letters in the other half.
With the blanks filled, four words appear in the grid, 3of 4 letters and 1 of 7..as I say, that's how I have interpreted the preamble. Hope this helps.