The plant we call Swiss chard in America is called silver beet in Australia. It's true that chard is the plant called Beta vulgaris, which is a family of beet varieties. Chard has beet leaves but no beet root — at least not one that we eat.
I just learned this morning that in British English chard is, or maybe used to be, called "spinach." Sometimes "perpetual spinach." It's a plant with complicated naming conventions in France too — in my experience, most people call chard by the name blettes. Purists, and some dictionaries, including the Larousse Gastronomique food encyclopedia, seem to prefer the term bettes, without the L, even though the Académie Française recognized the form blette as early as 1798 and again in 1835.
As for cooking, some people cook chard leaves whole, including the green part of the leaves as well has the thick, fleshy leaf ribs. Cooked, the green parts do resemble cooked spinach, but with a milder flavor. They're good cooked with some crème fraîche with a spoonful of moutarde de Dijon added. Or with olive oil and garlic. In France, people often cook the white chard ribs separately, either in butter, olive oil, or meat jus. They're also good au gratin, with béchamel sauce, cream, and/or melted cheese.
I'll be putting some chard leaves from the 2019 blette plants into a zucchini lasagna for today's lunch, with sausage meat, mushrooms, and tomato sauce. Chard leaves and/or ribs are also good baked in a tart or a quiche, or as as a filling for an omelet. This years springtime weather seems to have made the chard plants I planted last year happy and healthy — they survived our admittedly mild winter out in the garden plot just fine.