If the human lifecycle were alternation of generations, the normal adult human would be the sporophyte. Adult humans, of which there might be only one sex depending on which phylum of plants is used for the model, would emit spores from their genital organs which would fall to the ground, germinate, and grow into distinct, free-living haploid organisms (like gametophytes) or be retained by the body of the adult human female. These would produce gametes by mitosis which would find one another and fuse to produce a zygote. Then, this would grow by mitosis into a normal, adult human.
Work Step by Step
To get this question, just look at Fig. 29.3 to see the generalized land plant lifecycle. Put an adult human in place of the 2n sporophyte and create an analogy, as far as possible given the very different lifecycle humans actually have, by switching out plant stages for human stages you know or by inventing new stages in human development to replace plant ones for which there is no real human analog.