Step 1: Learn how.
You can teach yourself, buy a book, go online, or take a classroom class to fulfill #1 above. Depending on your natural aptitudes and skills, the rate at which you can learn will determine when (or if) you move on to Step 2.
Learning computer programming isn't a trivial undertaking, so you might want to ask yourself first what you hope to accomplish. If your hopes don't include writing more application programs (apps), you might be better off commissioning an already skilled programmer to develop the app for you.