Vocation means a call. It is God’s invitation, His call to each person to love and serve Him and His Church in a particular state or way of life. Each person's vocation flows from the grace of Baptism.
A man is ordained to Priesthood through the Sacrament of Holy Orders. Together each man and the Church discern (discover) whether or not he is called to become a priest. Diocesan priests a called to serve the people of a particular diocese. Men called to be priests in religious orders belong to communities and in addition to receiving the Sacrament of Holy Orders they also take vows of poverty, chastity and obedience (the three evangelical counsels.)