Becoming a dentist is a long but rewarding road. The first step is completing a four-year degree in some kind of pre-dentistry major (biology, chemistry, etc.). Some school offer a Bachelors Degree in pre-Dentistry specifically, so keep an eye out for that option at various schools.
After that, you'll need to take the Dental Admission Test (DAT). It typically takes 3-4 months of studying to prepare, but a lot of what you'll need, you'll learn throughout your undergraduate studies.
Once you pass you DAT, you can start applying to Dental Schools which take 4 years to complete a DDS. Depending on the school, your time will be split between lecture time and clinical practice. Some schools provide you with an opportunity to do a 'residency' which is typically a year and gives you the ability to specialize.
My best friend and former roommate is in dental school right now so let me know if you have any other questions!