Who is God?
Key Verse: In the beginning God created the heaven and the earth.  [Genesis 1:1]

God the Creator
God is the supreme being in the universe.  He created the heavens and the earth and He also created man.
In the beginning God created the heaven and the earth.  [Genesis 1:1]
And the LORD God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul.  [Genesis 2:7]
God is the one true God with absolute power.
But the LORD is the true God, he is the living God, and an everlasting king: at his wrath the earth shall tremble, and the nations shall not be able to abide his indignation.  Thus shall ye say unto them, The gods that have not made the heavens and the earth, even they shall perish from the earth, and from under these heavens.  He hath made the earth by his power, he hath established the world by his wisdom, and hath stretched out the heavens by his discretion.  [Jeremiah 10:10-12]
The LORD reigneth; let the earth rejoice; let the multitude of isles be glad thereof.  Clouds and darkness are round about him: righteousness and judgment are the habitation of his throne.  A fire goeth before him, and burneth up his enemies round about.  His lightnings enlightened the world: the earth saw, and trembled.  The hills melted like wax at the presence of the LORD, at the presence of the Lord of the whole earth.  The heavens declare his righteousness, and all the people see his glory.  [Psalms 97:1-6]
God the Father
The Lord God is our heavenly father.  He set the plan for our salvation into effect.
For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.  [John 3:16]
When we pray, we pray to God.  This is illustrated by the example Jesus gave us in how to pray.
After this manner therefore pray ye: Our Father which art in heaven, Hallowed be thy name.  Thy kingdom come. Thy will be done in earth, as it is in heaven.  Give us this day our daily bread.  And forgive us our debts, as we forgive our debtors.  And lead us not into temptation, but deliver us from evil: For thine is the kingdom, and the power, and the glory, for ever. Amen.  [Matthew 6:9-13]
The Lord God is the one true God of the universe.  He created man and set the plan for His salvation into effect by sending his only begotten son, Jesus Christ, to the earth.  God is the all powerful, all knowing ruler of all creation.