The primary way that the God of the universe speaks is through the Bible, what He has used human beings to write as they were carried along by His Holy Spirit.
“…but men spoke from God as they were carried along by the Holy Spirit.”
2 Peter 1:21
Another way that God speaks, is through His people:
“The one who hears you hears me, and the one who rejects you rejects me, and the one who rejects me rejects him who sent me.”