N00b-question: How do I stack two materials with the top one being an alpha texture?

I used to work in Cinema 4D, so I have to get used to the workflow of Blender. :slight_smile:
With my C4D-background, I prefer working with multiple materials over having a way too complicated Node Editor.
But how can I achieve this workflow in Blender?

Here’s the thing:

The rendered result I was looking for: a cup with a sticker on it. But I made this with one material, while I prefer working with two: one for the grey background color and one for the sticker.

The workflow I was looking for: two materials on this one object. But as soon as I made my face selection for the sticker, I lost the grey background color (it became black instead).

My face selection:

Anyone any idea?

Many thanks in advance! :stuck_out_tongue:

Nobody any idea?