A Christian is a person who is trusting Jesus Christ for their eternal salvation, and is seeking to follow Him in their daily life. To put it another way, a Christian is committed to Jesus as both their Savior and their Lord (or master).
Let me explain what this means. It means first of all that Jesus Christ was more than an extraordinary man; He was the unique Son of God -- fully God and fully man. As Jesus Himself said, "I and the Father are one" (John 10:30).
It means also that Jesus Christ was sent into the world for a purpose -- and that purpose was to save us from our sins. Sin separates us from God; it also makes us subject to God's judgment. But God loves us, and on the cross all our sins were placed on Christ, and He took upon Himself the judgment and Hell we deserve. When we commit our lives to Christ, God forgives us -- and now our desire is to live for Him instead of ourselves.
Only God knows if your friends have truly trusted Christ and are seeking to follow Him. But what about you? Are you trusting Christ alone for your salvation, and are you seeking to follow Him as the Lord of your life? Make certain, by committing your life to Christ today. The Bible says, "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" (Romans 10:9).