I am really not familiar with people who attended high schools in other countries, so my comments are mainly for someone who went to high school in the United States.
In order to go directly to medical school after high school in the United States, you'd have to get accepted into a combined BA/MD program. You can see more information about this programs in
this thread on combined BA/MD programs. In order to get accepted into these 6-8 year combined programs, you'd have to be at the top of your high school class. I really don't know if these programs even consider graduates from non-US high schools.
The traditional route for someone graduating from high school in the US is to go to a 4 year college and get a bachelors degree, and then go to a 4 year medical school. You have to do very well in the 4 year college and do well on the MCAT exam to get accepted into a medical school. The classes that you take at a 2 year college can count towards your bachelors degree, but you should NOT take the required pre-med courses at a 2 year college. Medical schools generally won't consider the 2 year college science classes as adequate to get into medical school.
At a 4 year college, you'd have to take 1 year of general chemistry with lab, 1 year biology with lab, 1 year organic chemistry with lab, and 1 year of physics. These should all be at the appropriate level for someone majoring in each of those fields. You can not take these courses at a 2 year college.
You would take your MCAT typically around your 3rd year of college so that you would have time to apply and interview at medical schools during your 4th year.
As you attended high school in another country, I'm not sure how easy it is to get accepted into a good 4 year college. Your first step would be to get into a 4 year college.
While I don't want to sound like a pessimist, if your grades were just above average in high school, then there is a good chance that you will have a very difficult time getting the necessary grades in college to get into medical school.