I want to know if I am in correct venue to teach me to write a software program that I can copywright and then sell to auto dealers combining their sales with a tax concept
This is certainly a good place to learn programming, which might assist you with your software. Start by downloading HH and trying the Lessons.
The development of a software package for a specific industry is well beyond what we can handle here and (as a software developer myself) I would suggest when you have an understanding of the programming involved, to look in your area for other programmers who might help beyond the basics we cover here.
Please keep asking questions though as you go!