Mormon theology teaches that God (the Father) , was once a man and is now and exaulted man and a god.
That Jesus is his first spirit child, with all of us being his (the Father’s) spiritual children. That includes Lucifer. (So in that way, Jesus and Satan are brothers and we are their brothers and sisters)
The “Plan of Salvation” is where human beings seek the highest level in the Celestial Kingdom, thus becoming Gods and Godesses. Kings and Queens, Priests and Priestesses.
That is called Exhautation and, at least in what used to be Mormon theology, men and women, as couples, become gods and goddesses of their own planets and continue the process. They set up worlds, have spirit children.
So (at least what used to be Mormon theology) There is God the Father, and he had a Father, and so on back thru infinity.
Think of it as a big large eternally family, going not only forward in time and eternity, but backwards as well.
(the following is an accurate account of what was Mormon theology when I was LDS. It is fair to state that Mormon theology has been changing in the past couple of decades)
en.wikipedia.org/wiki/Mormon_cosmology