There’s a wide range of techniques that will help you replicate a painting effect in Photoshop
Having a tablet will help because pen pressure helps you get more depth, and you can control adding in strokes a lot better.
Open a reference image and, on a new layer, trace some generic lines with a small hard brush. Don’t worry about following the edges exactly.
Use the pen pressure setting to fade in and out the strokes easily. Once you have the outline, create more layers underneath and start applying the base colour of your objects using a hard brush.
Once the base colour is set, use more layers to paint different shades of the same colour.
A lower brush opacity and flow will give the same effect as pen pressure, if you don’t have a tablet. Use Soft Light, Lighten or other blend modes and Levels and Curves adjustment layers to get the contrast you want.