This is subtractive rather than additive but I ended up following this video vaguely as a start when I was doing keychains. Cad packages weren't enjoying the vector image. I ended up creating an stl for the components (text, image and body) and merging them with a boolean operation, think this might help you get started as I had no idea where to even look.

At the very simplest, you can just overlap things in the slicer without Blender.

If you want to learn about Blender's Sculpt mode, you can just Google "Blender Sculpt mode tutorial". For convenience, try to use the most recent results, as the interface can be slightly different in older versions.

Sculpt mode effectively allows you to alter the models as if they were made of clay or plasticine.

A lot of the tutorials will be showing how to make things from scratch, but what's important is that you see how the tools work.

Once you have everything overlapping the way you want, you can join the using a Boolean operation. You'll want to use a "union" operation.