This being said, for newcomers it is important to understand that new actions need to be text coded.
The best way to do that is to watch a few videos about coding, such as Unity's series and a few other ones that might be specific to one's own requirements. Even if one doesn't understand the coding syntax, the tutorial should still be clear enough as to explain what is going on in the code.
Then, assuming you want to do something not too complicated, find the already existing PM actions that seem to do things similar to what you want and copy their code for further modifications into your own new actions.
Then, look at Unity's official scripting manual to see how you can talk to Unity in C# and also collect or set certain value types and transform that into Playmaker-friendly code.
