If you wander in a place, you walk around there in a casual way, often without intending to go in any particular direction.

If a person or animal wanders from a place where they are supposed to stay, they move away from the place without going in a particular direction.

If your mind wanders or your thoughts wander, you stop concentrating on something and start thinking about other things.

If your eyes wander, you stop looking at one thing and start looking around at other things.