Spirits make themselves known on the earth plane for two basic reasons. One reason is that the spirit itself considers it has unfinished work. But the second, and most usual, reason is that the person who is living in that property or frequenting the area is subconsciously calling the spirit.
A lot of people have not developed their ability to communicate with their spirits and guides and, therefore, when they find themselves in a position of actually facing a ghost or witnessing a ghost's activities they are unprepared. In many cases this causes fear, which emanates from the person on a vibrational level and bombards the spirit that has been called.
The spirit rejects this fear vibration and automatically hurls it back to the one who sent it. It is at this point objects may move, people sense a change in temperature or actually see the manifestations of the ghost itself.
Ghosts are normally harmless for the most part and have relatively no desire to bring harm to anyone nor do they have much of an awareness to act as such. There may be a few more mischievous human spirits that will do these things to bother you and scare you on purpose. They may just be a prankster or maybe they want you to leave the old home or not to change something in the home. These human spirits account for a majority of the hauntings we encounter and are relatively harmless. Yes, there are extreme cases and sometimes they can cause dangerous situations, but this is not the norm. To state it plainly, they are actually limited in the activities that they are able to carry out in their frame of existence. Most time, the "evil" that people feel at the time they see the black figures is the natural fear being misinterpreted as an evil presence. Many people are frightened by the normal symptoms of a haunting like footsteps, doors opening, voices, etc. They assume they are being hounded by demons from hell.
Other than typical symptoms of a haunting, there is little else the mean spirited human ghost can do to you except make you feel like it doesn't like you. In conclusion, seeing a black shadowy spirit does not mean that you are definitely facing an evil spirit.
Evil spirits and demons on the other hand, who have never had a body, have additional powers and have the ability to sway our thoughts and tempt our reasoning. Handle the Ouija Boards whith extreme care as it is has the power to open windows into other dimensions and attract evil or bad spirits.