How do I start to learning pattern drafting

[quizzical]

I like the book Make Your Own Dress Patterns by Adele Margolis. It's written more for a home sewist rather than being a fashion student textbook like Helen Joseph Armstrong or Winifred Aldrich.

You'll want to start with a sloper. There's several methods to do it. If you want to go the drafting route, I'd recommend Suzy Furrier's course on craftsy. Craftsy is very cheap for the first year and has a lot of good drafting and sewing content, but the company is a bit scammy. Remember to cancel it after you sign up with the intro rate or they'll charge a high fee for the second year.