Here's how I like to get the buttonhole placement on a shirt just right, tips on sewing buttonholes and a tutorial link to how to sew on a button.
Diary of a Sewing Fanatic: Shirt Sewing Tips
Sew Alongs and Tutorials
Olya Step 10 – Paper Theory Patterns
CREATING PERFECT Buttonholes – The Avid Seamstress
shirtmaking
Fitting Lines & Button Stands – Modeliste Creative
Sewing Glossary: How To Draft And Sew Concealed Button Bands – the
Shirtmaking: Button Placement & Buttonhole Tips
Quick Tip: Button Placement Inside a Vertical Buttonhole - Threads
How to sew a hidden buttonhole? — Couture Hacker
CREATING PERFECT Buttonholes – The Avid Seamstress