Also some of my garlic developed pods on top with what looks like "seeds" ?? Anyone know about these? Should I plant them and see what happens?

Last Fall I harvested some tiny little onions from my "seeds" from the Spring before. Are these what is called "onion sets" ??? I did replant them again this Spring already and they are growing. Last year I planted sets and I got some HUGE humongous onions--several six inches across! They were the yellow winter onions. And they kept really well all winter. I am down to my last few now.
But how do onions and garlic work from seed to final product?