Thats great, then you have time. So please keep somewhere in your mind that Hacettepe in Ankara, the capital city, is the best among English programs. Cerrahpasa is in Istanbul.
As for admission requirements they were admitting with SAT until this year, but this year Hacettepe goes on to admit with SAT (and some other internationally recognized tests), but many others admit either by SAT or their own aptitude test, YOS, or left SAT altogether and admit by only YOS. YOS is to check aptitude and some math(there are books for trial tests in English,
METROPOL YAYINLARI - METROPOL PUBLICATIONS - YÖS Deneme S). YOS has a Turkish part too, but its evaluated later. If you have a good score from aptitude part, but fail in Turkish, then you take a prep year to learn Turkish, thats mostly how they do it. At the time of your graduation you must check the changes in the system, and the details, there is still some time until then.
Out of those scores, the rest is classical paperwork: high school diploma or transcript, health report etc.