To develop Mediumship takes time, a lot of hard work and above all patience. Contrary to what all intensive weekend courses promises, there is nothing "quick" about Mediumship.
What is a medium then? A medium is just a regular person who has developed their senses for the possibility to communicate with people who have passed over to the other side. A medium's actual purpose is to provide proof of survival of the so called "death". When saying this you must accept that we might not be able to prove that we have eternal Life, but we can give as much evidence as needed for the person has come to consult us that it is enough evidence for them. By communicating with a person in the spirit world they can give us enough evidence that is needed for this to happen.
The most common form of mediumship is what you call 'Mental Mediumship' and that is when the Spirit World has the possibility to impress the medium through seeing, sensing and hearing. The medium can perceive this either objectively or subjectively, where one is not better than the other. In this way they can relay the information about the person, or spirit which they are in communication with and wishes to communicate with their loved ones left behind in the physical. This is demonstrated most often via a demonstration of mediumship or a private sitting with a medium.
The role of the medium is to relay evidence of survival, that life continues after the so-called physical death. Our soul lives on and through the contact with our loved ones who have already passed through the veil into the Spirit World before us, a medium can provide the personal evidence which makes us understand that this is how it is. A medium is not there to predict the future since nothing is cast in stone.
We have a great personal responsibility of our own lives and how we choose to live it. Our loved ones in Spirit would like to relay that they have made the journey over to the etheric realm and that they are well. They also naturally wish to make sure that we who are left behind in the physical are well too, and sometimes like to give a few tips and ideas of how to perhaps see things in a new perspective. They will not tell us what to do or how to think but like to provide a little encouragement to us.