I don't know when I first bought chard seeds, but it was also the first year I ever ate it. Chard is a fairly mild leafy green vegetable, similar in taste to spinach, but not quite as slimy when cooked. It also has a fairly thick stem, which tastes a bit like a mild beet.
I let my chard plants go to seed in their second year of growth, and have been collecting my own seed for many years now. This year I've had a few badly behaved plants go to seed in the first year: this trait isn't wanted and these plants are cut down and not allowed to flower. I want a full year of leaf production before seeds; making flowers/seeds stops the leaves from growing and the plant usually dies after.
On to cooking chard. With tender young leaves I will chop them, stems included, and add them to stews, stir fries, curries, casseroles. The older stems can still be eaten, but I usually strip the leaves off, chop the stems finely, and cook them first, adding the leaves at the end of cooking.
While I don't generally cook chard on its own as a side dish (because A. I'm lazy, and B. it's a bit boring), I sometimes saute it with some onions, garlic, a can of tomatoes, and any herbs I happen to have lying about.
I've also experimented with lacto-fermenting the stems (no leaves) with fresh garlic. Preliminary trials seems to indicate this is quite tasty. I just cut the stems into inch long pieces, chucked them in a jar with some sliced garlic, covered it with water and tipped in a spoonful of salt. Then I let it ferment, covered, on my counter for about a week. It tastes similar to a garlicky cucumber pickle, but with a hint of beet and goes great on a salad.