The plant life cycle includes the alternation of generations between two different mulicellular organisms, either of which might rightly be called a "plant." A diploid SPOROPHYTE (i.e., a spore-producing plant) produces haploid SPORES which develop into multicellular haploid GAMETOPHYTES (i.e., gamete-producing plants) that produce haploid GAMETES that fuse together to develop into a multicellular  diploid SPOROPHYTE.  

Here's a sketch, done by hand to introduce a human element, like it's a person talking. We could have made a fancy drawing with Photoshop that looked professional. Or stuck in another textbook figure. But this is down to earth.  Everything above the horizontal line is DIPLOID; below the line is HAPLOID. The big circle-ish things are plants.

PLANT (alternation of generations) LIFE CYCLE

Over evolutionary time, there's been a trend for plants to develop sporophytes that are larger and more important ecologically that their gametophytes. For most plants, when you see "the plant," you're seeing the sporophyte. A fern is a sporophyte, as is a pine tree or a daisy. But for the primitive bryophytes, it's the other way around. The green, leafy space-occupying entity that competes with other plants is the gametophyte. The bryophyte sporophyte is usually smaller, and simple, looking like an appendage of the gametophyte, to which it is permanently attached.  The bryophyte sporophyte lives as a parasite upon the maternal gametophyte that produced it. 

The picture below is of the moss Entodon seductrix showing both stages of the life cycle.  

Next: The Moss Life Cycle (and more hand-drawn figures).