How to use built-in tax feature?

[NekaDavaa]

Hi, in docs you mentioned to implement Taxable interface and use the HasTax trait, but where? I am just using the facade:

public function getSubTotal()
    {
        if (request()->ajax()) {
            return response()->json([
                'success' => true,
                'subtotal' => Cart::subtotal()
            ]);
        }

        return Cart::subtotal();
    }

Is there option to make model for that? Can you help me to use tax feature with the facade? Thankss