Christianity holds that God and Jesus are made of the same divine substance. This can be a little confusing, especially when we talk about the risen Christ who ascends to heaven.
In Christian tradition, the Holy Trinity is made up of three forms or incarnations of the divine- the Father, the Son, and the Holy Spirit or Holy Ghost. All three of these are made of the same "substance," God. Imagine if you were to take a ball of clay, and form it into different shapes. You can make the clay into a cup, a human figure, even a tool. Just like that one ball of clay can take different forms, Christians believe that God can take on different forms with distinct qualities. The form God may take is dependent upon what is needed of him.
Jesus is an incarnation of God- his divine substance existed before the physical form was born, and returned to Heaven after his death. Jesus represents the form of God the Son.
Perhaps the one major difference between "God" and "Jesus," is that Jesus was the physical form of God the Son on Earth. God on its own does not have a physical form, it is just the divine energy. Though Jesus had a human form, Christians believe his spirit was the same as that of God, and therefore he was divine.