You can read the thoughts of creatures. As your action, you can focus on one visible creature within 30 feet if it has an INT > 3 and speaks any language. You learn the surface thoughts of the creature. As an action, you can either shift to another creature or attempt to probe deeper. If you probe deeper, the target must make a WIS saving throw. If it fails, you gain insight into its reasoning (if any), its emotional state, and something that looms large in its mind. If it succeeds, the spell ends. The target knows that you are probing, and can use its action to make an INT check contested by your INT check. If it succeeds, the spell ends.
You can also use this to detect the presence of thinking creatures you can't see. As an action during the duration, you can search for thoughts within 30 feet of you. The spell can penetrate barriers (except 2 feet of rock, 2 inches of metal, or a thin sheet of lead). You can't detect INT <= 3. Once you detect a creature, you can read its thoughts, even if you can't see it but within range.