Having fellowship with other Christians is important for us after we believe in Christ; we need their encouragement, and they need ours. We'll also grow in our faith as we learn together from God's Word, and it's also good for us to come together to worship God.
But we aren't saved by simply joining a church -- important as it is to do so. Only Jesus Christ can save us, and our faith and hope must be in Him alone. You see, only one thing will keep us out of heaven, and that is our sin. And no matter how good we are, we'll never be good enough to get into heaven on our own, because God's standard is perfection. As the Bible says, "There is no one righteous, not even one" (Romans 3:10).
How, then, can we be cleansed from our sin? We can't do it ourselves; our sin is too great. Only God can forgive our sins and take them away -- and He made this possible by sending His Son, Jesus Christ, into the world to be the final and complete sacrifice for our sins.
By a simple prayer of faith ask Jesus to come into your life and take away your sins -- and He will. Then ask Him to guide you to a church where you'll learn from the Bible more about His love for you, and where you'll also meet other believers who can encourage and help you. May God bless you.