Piazza San Silvestro  is located in the hearth of the historical center of Rome.
From here, you can easily walk to:
There's a bus every 5 minutes or so, which will get you in the hearth of the Histotical Center of Rome in 5 minutes.
As usual, get standard tickets in advance at tobaco shop or news paper stands, or get a Roma Pass.
Most of time, just get a 75 minutes (1,5 Euro ticket) per way and you'll be allright.
Bus 80. Cheap, Easy and effective
by the Mignon cinema
41° 54' 42.0732" N, 12° 29' 53.5704" E