Just because someone can type and spell mononucleosis, doesn't make one cut out to be a Medical Transcriptionist. At the barest minimum, take a class in medical terminology.
Be prepared to sit for hours in front of a computer monitor. If you are a social person and need to be around people, this is not the job for you. It is very self-isolating.
Computers have made the transcribing much easier these days with the spellchecks and short forms and formating already prepared. The word processing program you use will depend on where you end up working. So, you will need to be a little familiar with several.
If you should go so far as to take a MT course, be aware that in the real world, dictators will not be as clear and as succinct in their dictations as they are in the practice tapes. You will get a wide variety of accents, you will get more than your share of mumblers, coughers, burpers, and you will also get doctors eating while dictating, driving their cars (convertible no less) and doing various other things while dictating.
MT is not an easy field to break into. Most places want someone with a minimum of two years experience but with luck, you may find the one place desperate enough that they are willing to train a suitable candidate.
I do not wish to discourage anyone from entering this field. It has been my livelihood for 28 years and it has served me well. It has many rewards and is always challenging. I have just seen too many women (and a few men) attempt to enter this field thinking it will be a piece of cake and then get totally discouraged. You have to be self-motivated and very determined -- especially if one plans on working out of the home.
I just wanted to make sure you have your eyes wide open when entering this field. It really is a great field to be in and I wish you luck and success. Feel free to PM me if you have any specific questions you feel I may be able to help you with.