professionals reply please!

Hi experts.
I am going to write a program for someone's dissertation.
It's my first official program that I want to write for someone else.

I want to know, Is programming on this level is as simple as for example double click on a button and write a code for it? (it was just a simple example)
What should I do to my program become better?
What should I do to reduce disadvantages of that, for example checking if one or more textboxes are in valid format or not?

Please Help me.
I may ask you more questions later.
Thanks