Obeying God's Call: The Order of Salvation

After hearing Peter's sermon the people are so stirred and convicted by their own sin that they cry out to Peter and the Apostles. Is there anything for us "to do" if salvation is of all of God? Peter urges them to repent and not to wait. What is the Ordo Salutis or order of salvation that Peter reveals through these verses? Are we involved or not?