Very good question!
Most pharmacists have at least a Bachelor of Science degree in chemistry or other science such as physics or biology. The PharmD degree that pharmacists receive upon graduation takes between 3-4 years of study. You will have to get excellent grades throughout high school and college to be considered for admission.
You may want to talk to a pharmacist to find out what she does at work.
I teach a course for pharmacy technicians at a community college, some of whom are planning to go on to pharmacy college.
Best of luck.
I agree with all above but certainly look into volunteering your time in a community pharmacy, hospital pharmacy,clinics etc during your junior year. By the time senior year comes and you are certain that is the way you still want, take most of the core science classes and your first year of college classes should include all your basics sciences with strong grades.
Your chances increases into pharmacy school after a college degree in the sciences, however going directly from high school is doable but has become increasingly challenging because of its competitiveness and demand.
After high school, you have to study at least 8 years, 4 for undergrads and 4 for the actual program. Even though, many pharmacy schools don't require undergrad degree, it increases your chance of admission. You can also do a residency of 1 to 2 years after pharmacy degree.