I have been told there is a difference. So what is the difference? I need help here :L

Also, Why can certain people see ghost/spirits and some others can't and they can't communicate with them.

A ghost IS a spirit. There are different types of spirits... angels, demons, human. The misunderstood thing is that the human spirits are never the ones we are in contact with.

Some people can contact/sense spirits because the SPIRIT allows them to. It has nothing to do with the person, but the ability given by the spirit.