He made darkness his secret place; i.e. he hid himself amid clouds and thick darkness. In executing his judgments he did not allow himself to be seen. God's action is always secret and inscrutable. His pavilion round about him were dark waters and thick clouds of the skies.
The original runs as follows: "He made darkness his secret place—his pavilion round about him—dark waters, thick clouds of the skies." The whole forms one sentence, "his pavilion" being in apposition with "secret place," and the last clause, "dark waters, thick clouds of the skies," being exegetical of the "darkness" in the first clause.
God's "pavilion," or "tent" ( סבּה), is mentioned again in Psalms 27:5 and Psalms 31:20.