People must "do" two things to be saved, though actually they may be considered one thing, part and parcel. The Scripture says it in various ways, but simply put, people must "repent" and "believe".
The essence of repentence is to change one's mind, or one's "beliefs", in this case regarding our sin and Jesus Christ as Lord and Savior. Changing one's mind includes at least some change in actions as well. One must believe in Jesus Christ as their Lord, or Master, and believe that He is alive, risen from the dead. And if one believes in Jesus Christ as their Master, they will at least to some extent live differently, as they follow Him. And believing in Him as Savior will ideally wipe away all faith in oneself as Savior, recognizing Him as the one who paid for sin, and said, "It is finished", then giving the righteousness of God to them as a gift.
So far, so good. But there is one little problem...
...People are born "dead in their sins and trespasses" (Ephesians 2:1). That means dead spiritually, and therefore they are unable to "repent and believe". Along comes Grace, in the form of the Holy Spirit, who "regenerates" some, gives them Life, gives them a new heart, gives them "the new birth", and they are "born again". Read John 3, where Jesus speaks to Nicodemus about this new birth, and one thing is clear. The Spirit, like the wind, blows where He chooses to blow (John 3:8).
And the newly "born again" ones are "new creations" (2 Corinthians 5:17). They are now "alive to God" (Romans 6:11), and with this new life, something amazing happens...
...They "repent" and "believe". They can't help it! It's been revealed, by revelation, and though they were blind, now they see! Their repentence and faith didn't even produce their regeneration, let alone merit it. Too often the cart has been put before the horse. Regeneration must come first. Jesus said that unless a man is "born again", he cannot even see(!) the kingdom of God [let alone believe in the King].
That's true Grace. All of Grace. All of God. The New Covenant, that glorious unilateral covenant in which God the Son becomes the sacrifice Lamb, then short-circuits any form of "works" salvation by giving new life to His children before they can do any "works". And they now believe in the One Who has been revealed to them. And as His new creation, the believer has all their sins forgiven, forever! So the Grace Goes On. And On.
Keep this Primacy of Regeneration in mind, and you will see many Scriptures opened up to your understanding like never before, I promise you.