Hi,
If you are an experienced programmer, the best way is to simply open the actions scripts and study the structure, it's simple enough to understand the concepts.
I never create a custom action from scratch, I always open the few actions that look like what I want and copy paste what I need from them.
then, to use the playmaker api outside actions, in components. you basically have only few needs,
-- get to an fsm to read or write to fsm variables ( plenty of threads on this forum on that)
-- send fsm events, ( also plenty of threads on that)
if you plan on working with the api a lot, I strongly advice to get the playmaker utils asset from the ecosystem, it will contains tons of little helpers to facilitate working with playmaker from scripts. I wrote these along the last 10 years, plenty of things to simply open and look, pretty mucch all the playmaker api is used in this asset. So it's a great source of learning.
If you have questions, simply make new posts on a very specific aspect, and ping me if you get no reply.
Bye,
Jean