A utility application can be filed as a provisional or a non-provisional patent application. A non-provisional patent application is the “main” application filing which is examined by the patent office. Once a non-provisional application is filed, no further substantive changes/amendments can be made to the application.
At an average, it takes 2-4 years to get a patent granted (after filing the non-provisional application), so filing the application is just the beginning of the process. Needless to say, it takes a lot of time and energy to draft a non-provisional application and selecting a qualified professional is important. Statistically, a non-provisional patent application that is not well written will most probably get abandoned during the examination phase.