Gametes always come from a gametophyte, and those always grow from spores. This is the absolute easiest. It's what we do. The gametes unite and form a zygote, which is what gametes everywhere aspire to do. The diploid zygote then grows up into a diploid adult, and it starts all over again.
Some organisms use one type of gamete, and can self-fertilize.
Gametangia are on the gametophytes, and they make gametes. Sporangia are on the sporophyte and make spores. If you see an organism that is supposed to have oogonium, you need to be able to find that, and tell me if it has an egg or zygote in it. Oedogonium is a good example of this. If you have trouble with this, contact me and we'll set up a review.