Where can I learn to create photoshop actions from scratch?

Where can I learn how to design complex photoshop actions from scratch like water color painting action, double exposure action, and things like that?
I’ve searched a lot on YouTube and Google and haven’t found anything helpful.

Do you mean actions I.e. the process, or do you mean the effects they authors deliver as actions I.e. the output/end result.

I mean how to create them from scratch to sell them on graphicriver

You can see how to record actions here Create actions in Adobe Photoshop (there are definitely many YouTube videos for this too).

You need to initially know what you want the action to do and how to achieve that.

How you learn this will depend entirely on what you are making happen, as no two actions are going to follow the exact same sequence.

It’s also better if you can create an effect/output which is unique to your process/steps, otherwise you are going to have a problem with making the item original and premium enough.

Bearing in mind that this is a premium marketplace there’s an assumption tht anyone wanting to sell items has the experience to develop their own creative effects and designs.