The 'Tangent' of a curve is determined by its geometry. There's only one vector which is tangent to a curve at any point.
That leaves a disc of (an infinite number of) possible 'Normals' to the curve, in the plane to which the Tangent is normal.
Which one of those is selected to be the 'Normal' at Tilt 0° is calculated internally, according to your curve's settings, as answered here.
The 'Tilt' is an angle about the 'Tangent' axis with respect to the pre-calculated Normal at Tilt 0°, to which the 'Normal' is then set:
So to get your cube to follow the tilt, you align one of its axes to the Normal....
... which may or may not have been tilted in your GN tree by Set Curve Tilt. (That angle can be varied along the curve, by feeding it some function of Spline Parameter, for example.)
You can rotate the vector to which your object is aligned around the Tangent 'by hand', as well.. the blue boxes above do much the same thing. One of them changes the Normal, the other changes your object's rotation with respect to the Normal.