Short answer is, they don't. Long answer is they rely on the ideomotor effect. It is so easy to move the rod that even barely noticeable movements will effect the direction it turns. Basically the user of the rod is subconsciously guiding it themselves.

Ouiji boards are harmless as long as the users know how they work. Spirit boards work on a psychological principle called ideomotor effect. There are no spirits or demons involved. Basically, the body moves according to the intent of the user(s). To get a spirit board working you (or at least one of the users) has to expect the pointer to move.

Once you and some friends get the pointer moving you'll notice that it quickly spells easily recognizable words and misspells any words that you would misspell.

For more fun, have someone change the orientation of the board while the users are blindfolded and then record what they spell.

Wikipedia has a good article on Ideomotor Effect.

Ouiji boards are harmless as long as the users know how they work. Spirit boards work on a psychological principle called ideomotor effect. There are no spirits or demons involved. Basically, the body moves according to the intent of the user(s). To get a spirit board working you (or at least one of the users) has to expect the pointer to move.

Once you and some friends get the pointer moving you'll notice that it quickly spells easily recognizable words and misspells any words that you would misspell.

For more fun, have someone change the orientation of the board while the users are blindfolded and then record what they spell.

Wikipedia has a good article on Ideomotor Effect.

If you want to know "how it works", it works based on the IdeoMotor effect: not spirits and ghosts of days past. Remember it is a GAME and a TOY developed and manufactured by a game and toy company.

The ideomotor effect refers to involuntary and unconscious motor behavior. The term "ideomotor action" was coined by William Carpenter in 1882 in his explanation for the movements of dowsing rods and pendulums by dowsers, and table turning by spirit mediums. The movement of pointers on Ouija boards is also due to the ideomotor effect. It's just a toy.

The ghost or paranormal person moves it

it guides you to its words