Usually you apply to get the tech license, then buy a book to study for the test, and if you pass you become a certified tech. Depends on your state which test they accept for certification so I'd look that up.
Where I work certification (exam) is not required, but you get paid a little more if you're certified. Then every 2 years you have to re-certify to keep your certification, all it takes is to study for 20 hours, there's no exams, just easy quiz.
Some states require certification, some state require formal education, meaning you gotta enroll into pharmacy tech college program, pass the exam, then you're certified.
Best thing would be to go to one or two local pharmacies and ask the pharmacist or technicians, they will guide you.
You can google "requirements for pharmacy technicians in (name of your state)", that's what I did!
Also, type in google something like "(name of your state) Board of Pharmacy", for example "Ohio Board of Pharmacy", there will be info on how to become certified.