how do i put a rail molding on a pony wall?

[james polk 1]

Actually I have a pony wall and the cap i am wanting to place on top is a 4" cap that tapers to a 2"cap in front

we ( my boss) and i have been trying to keep up the pace and learn this program at the same time.

We decided for visuals the cap in one of the molding libraries was exactly what was needed to be there.

How would i place that on there from some other library? and have it act as it should?