How are posters like these made?

Here's a few example of the style of poster I'm asking about.

1 2 3 4 5 6 7

Now, I'm assuming you need to know how to draw/paint to make these, and I'm not a complete stranger to that. But what is the actual technique used. Are these nowadays done completely digitally or is it better to actually paint/airbrush them. How well do actual painting skills transfer to digital? Does this style have a name? Are there tutorials?

I guess my main question is: If I want to start learning this, what do I actually start learning?

Great design resource

100 Things Every Designer Needs to Know About People (Voices That Matter) Submitted April 26, 2019 at 11:35PM by Mesha8 http://bit.ly/2GLp5eL