I strongly agree with the recommendation of the Word MVP page. I found the Udemy courses by Grant Gamble useful. A very good, if older, book is Writing Word Macros: An Introduction to Programming Word using VBA: PhD Steven Roman. A more general one is Mastering VBA for Microsoft Office 365: Richard Mansfield: 9781119579335: Amazon.com: Books.

To effectively program Word (or other applications) a strong feel for the program itself and how it does things is essential. Otherwise, you will find yourself trying to reinvent the wheel.

• Basic Concepts of Microsoft Word - from Shauna Kelly
• How to create numbered headings or outline numbering in Ribbon Versions of Word by Shauna Kelly
• Mailmerge Tips & Tricks
• Change Default Settings by Suzanne Barnhill, MVP
• Templates in Microsoft Word
• Importance of Styles in Word
• VBA Code Examples (3) by Graham Mayor, MVP
• Word Content Controls by Greg Maxey
• Repeating Data (Populating Multiple Like Fields) by Greg Maxey
• Dealing with Fields in Microsoft Word
• Word Numbering Explained by John McGhie, MVP
• Microsoft Word Field Maths Tutorial