You can read the thoughts of creatures. When you cast the spell and as your action on each turn, you can focus your mind on any one creature that you can see within 30 feet of you. If the creature has an Intelligence of 3 or lower or doesn't speak any language, it is unaffected.
You initially learn the surface thoughts of the creature - what is most on its mind in that moment. As an action, you can either shift your attention to another creature or attempt to probe deeper into creature's mind. 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 (such as something it worries over, loves, or hates). If it succeeds, the spell ends. The target knows that you are probing into its mind, and unless you shift your attention to another creature's thoughts, the creature can use its action on its turn to make an Intelligence check contested by your Intelligence check. If it succeeds, the spell ends.
Questions verbally directed at the target creature naturally shape the course of its thoughts (interrogation).
You can also use this to detect the presence of thinking creatures you can't see. When you cast the spell or as your 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 a creature with an Intelligence of 3 or lower or one that doesn't speak any language.
Once you detect the presence of a creature in this way, you can read its thoughts for the rest of the duration, even if you can't see it, but it must still be within range.