Missing principled idea

I had two slow time control games against my good man drfrankenstein on FICS. Here I am steering the rather sterile technical endgame to finish and missing two principled ideas.

If I move a piece, how will my opponent responds? In chess is this idea of response that somehow drops from my limited understanding.

If I want to be more specific: I always give squares and get squares while moving a piece. Which squares will I give?

Black to move and loose

s

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Ten points and a parrot sticker for the one who finds my move.