Contrary to what another responder said, I would not suggest reading Darwin first except for historical reasons. His book, while important, is outdated.
There has been so much learned about evolution during the past 150 years that, if you really want to learn about the subject, you should stick to recent publications.
The Greatest Show on Earth would be a good start.
And, of course, you can ignore any suggestions to read books by creationist authors. They are filled with deceit and outright lies. [Edit: The responders who call themselves truthseekers provide good evidence of that.]
Added
Some of Darwin's observations are still important. But, again, to learn about evolution, more recent books should be read.
Incidentally, as a med student, you might be interested in taking a look at my response to this question.
https://answersrip.com/question/index?qid=20110824112826AAcMyoJ
And @Truth Seeker (what a misnomer), evolution is both fact and theory. Evolution is what happens. The theory of evolution is an explanation of HOW it happens.
And the fossil record most certainly DOES support evolution, as does genetics and comparative anatomy. Though you claim to be an agnostic and that you have studied evolution for 50 years, you don't know squat about it and apparently go to lying creationist sources for your misinformation.
http://www.talkorigins.org/faqs/comdesc/hominids.html