Depending on how much general programming knowledge/skill you have, there are different approaches to go. Unless you are to take programming as your main career goal, there probably is no need to pay for learning VBA for AutoCAD, as a skilled AutoCAD user.
There are a lot of resources on the Internet for you to get started. You can simply search YouTube for "VBA programming AutoCAD", which would lead you tons of tutorials. To be warned: at this late game of AutoCAD VBA, as starter, most of those tutorials are quite old (base on 32-bit AutoCAD). So, your learning should be limited on basic concepts and simple UI (user interface items) included with current 64-bit VBA.
Unless you have known and determined well your programming learning objectives well, you may also want to look into LISP programming, or Dynamo (especially as certified C3D professional, well, with that, you'd better have some basic/generic programming knowledge).
Many, if not most of, AutoCAD programmers, me included, started AutoCAD programming by self-teaching, and the free online resources are abundant enough to get one started, IMO.