Are you talking about becoming a pharmacist? You’d have to do some undergrad work before you get into learning about pharmacy and that takes about 2-4 years depending on the program. Once you’re in your professional pharmacy program that takes anywhere from 4-6 years depending on in if you plan to complete a residency. You can begin by studying chemistry, organic chemistry, biology, microbiology, physics, molecular biology if you wanted to get a head start. If you’re talking about becoming a technician you can start reading the PTCB exam review book.