Anyone, anytime, anywhere can become a Christian if he/she takes one fateful step: "if you confess with your mouth, 'Jesus is Lord,' and believe in your heart that God raised him from the dead, you will be saved. For it is with your heart that you believe and are justified, and it is with your mouth that you confess and are saved." (Romans 10:9-10) Race, nationality, age, gender, none of them make any difference. What a person has done in the past, doesn't make him/her more or less capable of being saved if that person comes to God in faith. The most innocent child among us (though still a sinner as are we all) can be saved, as can the most hardened and vile criminal, for all alike need to be forgiven, and the blood of Jesus Christ is capable of cleansing anyone.
Work is not necessary to become a Christian, in fact, trying to work to earn salvation is a sure-fire way to fail to find it. Salvation is an act of God's grace, given to mankind through faith in Jesus. No specific words must be spoken, no setting or place is necessary, genuine faith will be sufficient. When one of the thieves being crucified alongside Jesus showed that he believed in him by saying, "Jesus, remember me when you come into your kingdom." Jesus responded to this man, a criminal hours away from death, by saying, "I tell you the truth, today you will be with me in paradise." The thief had no chance to earn God's favor, he had no chance to make up for his past, he simply called out to God for mercy, through Jesus, and he found it.
To be a Christian requires several things, again, these things do not help anyone become a Christian, they merely confirm what God has already done for that person through grace. If a person lacks these character traits/qualities, the Scriptures tell us that such a person may not have yet become a Christian, which would take us back to square one, the need for an act of faith. There are people who believe themselves to be Christians erroneously (and thus extremely dangerously) but who are in actuality not Christians at all, having evidently never believed in Jesus Christ.
The Bible calls the character traits/qualities of a Christian his/her "fruit". Jesus was quite clear in the Gospels that someone claiming to be a Christian without any evidence of "fruit" cannot be one. "I am the true vine, and my Father is the gardener. He cuts off every branch in me that bears no fruit, while every branch that does bear fruit he prunes so that it will be even more fruitful." (John 15:1-2). Jesus' brother James reiterated this point when he wrote, "What good is it, my brothers, if a man claims to have faith but has no deeds? Can such a faith save him?...faith by itself, if it is not accompanied by action, is dead." (James 2:14,17)
The "fruit" required of each and ever person who would be a Christian is explained in a variety of ways. Paul utilized a list, calling it the "fruit of the Spirit": "love, joy, peace, patience, kindness, goodness, faithfulness, gentleness and self-control." (Galatians 5:22) Not that any Christian has each and every one of these perfectly, but this is the character that demonstrates the fruit that Jesus warned us we must have once we have become Christians. We haven't mastered this list, but we sure better be working on it.
The Apostle John answered the question, "Who is a Christian?" in his first epistle by emphasizing three primary qualities and repeating them each over and over. John explained that all Christians must: (1) believe that Jesus is the Christ, the Son of God, (2) obey the commandments of God found in Scripture, and (3) show love for fellow brothers and sisters in Christ. John explained that anyone who could demonstrate these three should have no fear concerning their relationship with God for they are impossible to achieve for anyone who is not empowered by the Holy Spirit as someone who has already become a Christian. {This should be obvious, nobody can be a Christian who did not previously become a Christian. Faith must come first} The converse is also true: anyone who lacks one of these three should be rightly concerned that he/she must be truly be a Christian.
If you're interested in learning much more about what John has to say about the question, "Who is a Christian?" I wrote a 155 page book on the subject which you are more than welcome to read, it is entitled Christianity's Big Tent: The Ecumenism of I John and can be found via the link.
Let me summarize the distinction between becoming and being a Christian:
Become: anyone, by grace, through faith, in Jesus.
Be: Obey the Scriptures, believe in Jesus, love fellow Christians (i.e. "bear fruit")
To be a Christian is no easy task, Jesus likened it to each of us taking up a cross of our own and following him. In light of the difficulty of the road ahead, anyone who desires to be a Christian ought to be doing so as part of the fellowship of a local church where the Word of God is respected and followed and people build each other up through service and prayer. It is beyond the ability of virtually all of us to be a Christian who bears much fruit on our own. We need to be a part of a church. We need to be corrected when we err, we need to be supported when we stumble, we need the opportunity to grow by serving others, and lastly, but very importantly, we need to worship God with the people of God.
You don't need to be perfect to become a Christian, which is a relief since nobody is anything close to perfect. You don't need to be perfect to be a Christian either, which is a relief since none of us are perfect either, but you do need to be making progress. A "Christian" who bears no fruit, is no Christian at all, that's not my idea, but a very serious warning from Jesus himself.