Mediumship is the ability to perceive the spirits of those who once were physically alive and have now crossed over to the so-called other side. I believe that we all have this ability to some degree or another, or that we can all develop this ability in some way.
Traditionally, mediumship is done without any external tools, such as Tarot cards or runes, but is done entirely through the spiritual senses and their connection to the physical body.
Not all types of mediumship are the best fit for every person. Make sure you know what you're looking for and how to avoid what you're not looking for. Any spiritual worker who makes you feel scared, intimidated, or tries to guilt or shame you into taking any type of action is not someone worthy of your time, your money, or your attention.
This is the traditional style of mediumship, where your medium tells you they sense or see a man/woman/adult/child, give you an age, a method of passing, an object you can identify, describe a memory or recent experience, etc. An evidential medium gives you evidence that they are connecting with someone you can recognize on the other side.
This is a non-traditional style of mediumship where your medium uses psychic ability and/or connects mediumistically with the spirits of physicians who have crossed over to scan your body or get information related to your health. This should be a supportive and supporting experience; your medium should not use any kind of intimidation tactic or scare tactic. This also cannot be considered a replacement for medical treatment or medical diagnosis - please make sure that you are working with appropriately licensed medical professionals.
This is a non-traditional style of mediumship where your medium uses a combination of mediumistic and psychic ability to connect with spirit guides (who are not the spirits of people you would recognize from before they crossed over) and/or look into the future/past. Usually, a psychic medium will try to give you guidance around living your best life so that you can fulfill whatever purpose(s) you were born into this lifetime to fulfill.
...predicting the future (that's psychic - see above), connecting to your spirit guides (beyond your crossed over loved ones who guide you from the other side), or anything about a loved one being "stuck" or "in hell". Mediumship should be a healing experience; the spirits who come through should be able to provide evidence that you can validate to prove that they are who they claim to be; the messages they convey should be supportive and helpful. An ethical medium will NEVER tell you that someone is going to die or that a spirit is in "trouble" and needs you to pay money to "free" or "liberate" them.