Simply bezel the cup over the stone using a Bezel Rocker and Burnisher until your stone is held securely in place.
Then choose your size of Bezel Cup and a Cabochon in the corresponding size. Note that you will still need to check that the Cabochon fits inside the Bezel Cup.
Tip: You can use Binding Wire to help hold the pieces together whilst you solder, or a Third Hand Tool is a great trick.
Clean your piece by dropping it in Pickle and then use a Bezel Rocker to push the silver against the stone gently. Use a Curved Burnisher to smooth the edges around the Cabochon and ensure it is sitting in the Bezel Cup securely.
Polish your piece with Polishing Papers or Sanding and Polishing Sticks and shine up with a Jewellery Polishing Cloth to finish.