So, you are just beginning your undergraduate degree!
There are many things to consider, during this first year of university. First of all, about 2/3 of your first year bio class is planning to go into medicine. Be prepared for that, it can be a bit shocking!
So, the first big challenge is to start thinking about a program of studies. Classical wisdom states that you should probably do a degree in Biological Sciences, and this is a very viable approach. However, it is important to note that the med schools (by and large) do not care what your degree is in as long as you complete all of the necessary prerequisite courses. Keeping in mind that the single largest selection factor is grades, you may wish to consider taking an easier program of studies and fulfill the prereqs as options. For example, a bio major might take 3-4 difficult science courses and 1-2 easy options per semester; conversely, a social science or humanities major could take 3-4 easier (core) courses and 1-2 science courses (as options) and still finish the required prerequisites by the end of their program. So, the bio route is a good way to go, but consider your options. Remember, in this game GPA is everything!
Almost all of the schools (whether it is officially stated or not) expect that you will have completed some pretty serious volunteer work by the time you apply. Health related positions are preferred, and development work is good as well. Most hospitals have volunteer programs, as do many outreach and special needs agencies. The more hours you have the better and some programs have waiting lists, so get on this early. Many applicants will have hundreds of volunteer hours, so don't miss out on this one.
MCAT
If you are planning to apply to medical school after two years of university (this is allowed at most schools) you will need to write the MCAT this summer. Otherwise, worry about that demon later.
General
Overall, not a lot to do this year. As always, keep those grades up there! Start tackling the prerequisites early, you want as many completed as possible by the time you write the MCAT. Try to maintain some hobbies or sports, the selection committees like to see well rounded individuals.