Father is, of course, metaphorical. It reflects a hierarchy taken from patriarchal societies, including the way ours has been traditionally. In a society with a different understanding of sex and power, it could be Mother, it could be Parent. In context, it says at least two things to us.
First, that we have an inborn relationship with the One in authority.
Second, in the late Greco-Roman world, this someone in authority is a father, meaning nothing remotely close to a post-1990 nurturing New Age father. The ancient father was a man who had power of life and death over, and legally owned, every creature and person in his household.
God as father is a paradox, then, intimate in relationship, distant and awe-inspiring socially.
the Almighty, maker of heaven and earth,
It took until the middle ages before philosophers came up with a comfortable word to refer to the characteristics of God affirmed in the context of faith: attributes. No one has dissected God in biology class and described the divine entrails. Most of us have never seen God with our eyes. At best, we attribute traits or behavior to God, from what we can discern about divine deeds.
Almighty is an attribute referring to the idea that God must be the ultimate in every respect, or else whatever is the ultimate is God instead. In a patriarchal imperial society the almighty was the emperor. The Creed says, no, it is God.
The Nicene-Constantinopolitan creed has "maker" whereas the Apostles creed has "creator." The difference reflects a more close harmony with the biblical text, which suggests that God was working with something (a formless or void or trackless waste). Only the deuterocanonical Maccabees 7:28 says "from nothing."
Indeed, as an editor I usually cross out create, used to mean establish, set up, generate. Sorry, Republicans, there are no job creators among us, only job generators.
of all that is, seen and unseen
Yet, make no mistake about it, the council fathers added "all" to make sure no one misunderstands. The maker of all is, in effect, a creator. Indeed, causa causarum (cause of all causes) is the best-known phrase affirming a single deity and it is the one that even the big bang theory does not undo. Whatever matter banged did not preexist God, per the Creed.