From the website of International Medium Sandrea Mosses:
Ouija boards are not new and have been around since the 1890ís.
How do they work? The idea is that two or more people place a finger onto the planchette. The fingers lie loosely on the object to give it freedom to move. The participants ask the board a series of questions and in theory the planchette then floats across the board and slowly answers each question, by painstakingly moving from letter to letter or to the numbers giving answers to the questions.
Do they really work? Absolutely. How? By focusing our attention onto one small area, we are giving that space energy. This power does one of two things. It opens up a space between here and the afterlife and it gives power to entities and spirit people to be able to communicate with us. Spirit people donít need this power, but less desirable entities do. A very frightening aspect of this is that we are giving anyone the opportunity to communicate with us, including some very undesirable entities. This open invitation is equivalent to throwing open the front door of your house and inviting anyone in or freely advertising a party on one of the social network sites. Unless you were hoping to invite trouble into your home you wouldnít do it. So why do it with a board? It is a recipe for disaster and something you may regret for a long time. Unlike the party, this aftermath and fall out from this invitation can take a long time to clear up.