Before you can discover God's calling for you specifically, you must have a personal relationship with Jesus Christ. Jesus offers salvation to every person, and he wants to have an intimate friendship with each of his followers, but God reveals a calling only to those who accept him as their Savior.
This may put many people off, but Jesus himself said, "I am the way and the truth and the life. No one comes to the Father except through me." (John 14:6, NIV)