When we believe in Christ as Lord and Savior, not confessing him alone, but also believing in our hearts (there are many who confess but do not truly believe, God knows their hearts), we are saved. Paul attests to this:
RO 10:8 But what does it say? "THE WORD IS NEAR YOU, in your mouth and in your heart"that is, the word of faith which we are preaching,
RO 10:9 that if you confess with your mouth Jesus as Lord, and believe in your heart that God raised Him from the dead, you will be saved;
RO 10:10 for with the heart a person believes, resulting in righteousness, and with the mouth he confesses, resulting in salvation.
RO 10:11 For the Scripture says, "WHOEVER BELIEVES IN HIM WILL NOT BE DISAPPOINTED."
How are we as unregenerate sinners, unable to come to the Lord on our own, come to this saving faith? Because God calls us. Paul again explains how this happens:
RO 8:28 And we know that God causes all things to work together for good to those who love God, to those who are called according to His purpose.
RO 8:29 For those whom He foreknew, He also predestined to become conformed to the image of His Son, so that He would be the firstborn among many brethren;
RO 8:30 and these whom He predestined, He also called; and these whom He called, He also justified; and these whom He justified, He also glorified.
RO 8:31 What then shall we say to these things? If God is for us, who is against us?
RO 8:32 He who did not spare His own Son, but delivered Him over for us all, how will He not also with Him freely give us all things?
RO 8:33 Who will bring a charge against Gods elect? God is the one who justifies;
I hope that this answers your question.