Article 1 of the Augsburg Confession asserts, "We unanimously hold and teach, in accordance with the decree of the Council of Nicaea, that there is one divine essence, which is called and which is truly God, and that there are three persons in this one divine essence, equal in power and alike eternal: God the Father, God the Son, God the Holy Spirit. All three are one divine essence, eternal, without division, without end, of infinite power, wisdom, and goodness, one creator and preserver of all things visible and invisible. The word 'person' is to be understood as the Fathers employed the term in this connection, not as a part or a property of another but as that which exists of itself. Therefore all the heresies which are contrary to this article are rejected. Among these are the heresy of the Manicheans, who assert that there are two gods, one good and one evil; also, that of the Valentinians, Arians, Eunomians, Mohammedans, and others like them; also that of the Samosatenes, old and new, who hold that there is only one person and sophistically assert that the other two, the Word and the Holy Spirit, are not necessarily distinct persons but that the Word signifies a physical word or voice and that the Holy Spirit is a movement induced in creatures." (Augsburg Confession I.1-6 Tappert).

If you do not have a Book of Concord, I would recommend that you get one as soon as possible. After reading this from the Augsburg Confession, you can read the Apology to the Augsburg Confession article 1, and also read Luther's Smalcald article on his confession concerning God. However, the greatest thing you can read to understand who God is for you it the Large Catechism on the Creed. These words will offer greater comfort than I can write down here. Read how God creates you, rescues you, and makes you holy, all according to His grace and mercy toward you. 

Peace be with you. May the devil be silenced, the world be hushed, and the Old Adam be drowned anew so that you hear only the peaceful voice of your Savior Jesus who says, "I forgive you. I love you. I claim you as My own forever," Amen.

Jesus' Sheepdog