The main international airport at St Petersburg is Pulkovo 2.There is an airport express bus that will take you to the city, as well as two local buses but they will take longer to travel the route as they stop along the way.
Taxis to the centre of town will set you back a bit, just make sure you agree on the fare before you get in.
The easiest way to get around the sprawling St Petersburg is to use the metro.
It’s good value, is colour-coded like the Tube and trains come frequently. Although it can be a bit difficult to read the Russian signs of where you want to go.