Quick Bus Guide From Home To Downtown:

Bus Tickets cost 1,50 Euro and last 100 minutes from the time you validate them.
Same tickets are also valid for Metro transportation, but going toward one direction only.

Trevi Fountain, Piazza di Spagna, Downtown Shopping Area: Bus 80 or 80B until final stop in San Claudio: walk for about 4 minutes.

Piazza di Spagna, Downtown Shopping Area: Metro B1 and commute at Termini Station to Metro A, direction Battistini.

Get-off after 2 stops at Spagna.

Piazza Navona and Pantheon: Bus 80 or 80B until final stop in San Claudio: walk for about 7 minutes.

St. Peter's Church: Metro B1 or Bus 38 until final stop at Termini Station. Commute to Bus 64 (beware of pick-pockets on this Bus). to reach St. Peter's Church

OR
Bus 80, until Piazza Barberini stop, then Commute to Metro A, direction Battistini. Get-off after 4 stops at Ottaviano Station and walk for about 8 minutes to St. Peter's Church.

Vatican Museums and Sistine Chapel: Bus 80 or 80B, until Piazza Barberini stop, then Commute to Metro A, direction Battistini. Get-off after 5 stops at Cipro-Musei Vaticani Station.

Coliseum and Roman Forum: Metro B1 Get-off after 8 stops at Colosseo Station.

Piazza Venezia and Capitolium Hill: Bus 84 from Viale Tirreno until Piazza Venezia or Piazza Aracoeli.

Termini Station:  Metro B1 or Bus 38 until final stop.