Your private tour guide will meet you in the lobby of your hotel holding a sign with your name on. Afterwards you will discuss what you will going to see. You can then set off for your tour and let your guide fill you in with all information possible.
As much as you can decide what you want to see, here are some highlights that you should not miss: Church on the Spilled Blood, St Isaac's cathedral, Peter and Paul Fortress, Hermitage, Russian Museum, Alexander-Nevsky Lavra, River and Canal tour and others. You will end your half-day tour at a location of your choosing.