This is done in Photoshop or any other programs?
The picture is simple: a darkened photo, on top, this is possible even in paint to create. The primitive algorithm like this: throw a picture on top of a translucent dark rectangle on the upper layer of the diagram.
Do this for services online?
Online image editor then?
And generally a lot of them
This is a Digital drawing or just an ordinary graphics?
The question is a bit meaningless: any graphics displayed by the electronic device is a digital image of a format and type.
What to study to be able to create such an illustration?
Open the figma (link above), throw back a picture, create a rectangle on top, make it dark, give him clarity, download from Google scheme request scheme like transparent png (or freepik.com), throw it on top of (if necessary, reverse the colors), parse it and exportny in jpg/png. All.
If you need something more complicated - Google lessons, a lot of them free on the Internet, on YouTube including.