Can you post an image or something that will help us know what you're asking? What were you expecting, and what did you get, or not get, instead?
If you just want to use the brush, you can control all aspects of the brush, including brush softness, opacity, mode (normal multiply, etc.), color, etc.
You can also use a tablet that allows opacity, etc., according to pressure.
This is probably my most used method:
The primary object exists on its own layer.
On a new layer above it, I paint with white for highlight, or black for shading.
I use Gaussian blur on the highlight or shade layer — it is OK to let it overlap.
I Ctrl/Cmd click the primary object layer to load it as a selection, and with that selection active, add a layer mask to the highlight or shade layer.
Unlink the layer mask so you can move the shade or highlight. Reduce opacity if too strong, or duplicate the layer if too weak.
Other wrinkles I use are:
Set a shade layer to Multiply. And maybe a highlight layer to Screen, but that will make it very bright.
Or I might Ctrl/Cmd click the primary layer, and stroke the selection on a new layer above the primary layer using Center. Then blur the stroke, reload the selection and add a layer mask.
You can also fine tune using Mask properties. This is useful because feathering a mask will further soften the shade edge, but is non destructive. You can go back to mask properties and make more adjustments.
I find the above a more flexible approach than the usual dodge burn techniques, or even D&B on 50% grey layers set to Overlay.
Two more things I'll add is that if you don't have a steady hand, use the Pen tool to run a path that you can stroke, or if you are OK but want to be better, go get Lazy Nezumi Pro. It turns the shakiest hand into a master artist.