God reveals Himself in a general way through creation and our conscience. But we only know who He is as revealed Himself to us in His Word, the Bible, and His Son, Jesus Christ. The Bible tells us that we are all lost forever because of sin. But in Christ there is salvation from sin. He loves us so much that He died on the cross and rose from the grave to give us eternal life in heaven. God is one God, and yet, though we are not able to comprehend it, He is triune, which means that He is one God in three Persons and three Persons in one God: Father, Son, and Holy Spirit.
A summary of our beliefs is found in Luther's Small Catechism. The Catechism contains the core beliefs of Christianity, as taught in the Bible.
2. The Creed -- The Creed presents us with the Gospel, which is the message that God saves us from sin through His Son Jesus, who was born under the Law, kept it completely, suffered and died in our place, and rose from the grave so that we may live with Him forever in heaven. John 3:16; 1 Corinthians 15:3–7
3. The Lord's Prayer -- In the prayer He gave to the Church, our Lord teaches us not only how to pray, but godly living. Convicted by the Law, saved by the Gospel, we now live new lives according to God's will. In the Lord's Prayer we learn what that will is. Matthew 6:9–13; Luke 11:1–4
4. The Sacrament of Holy Baptism -- Baptism is one of the ways God forgives our sins and gives us new life. Baptism is spiritual birth, where we are given eternal life. Matthew 28:19–20; Romans 6:1–11; Titus 3:4–7
5. Confession -- Having been born anew, we now grow and live in the new life our Lord has given us. We sin daily and so are in need of confessing our sin daily. But God is merciful and forgives us abundantly. John 20:19–23
6. The Sacrament of the Altar -- This is the spiritual sustenance and nurturing our Lord gives us in the new life He has given us. In the bread and wine of our Lord's Supper He gives us His body and blood for the forgiveness of our sins and the strengthening of our faith. (This is also called the Lord's Supper, Holy Communion, and the Eucharist.) Matthew 26:26–29; Mark 14:22–25; Luke 22:14–23; 1 Corinthians 11:23–26