In the spectrum of greens, Chard lies between spinach and kale — not as tender as spinach, not as tough as kale. But like spinach, you can easily sauté it in some olive oil in just a few minutes.
The stems can be tough. You can either remove them and discard (or boil and toss with butter), if some of the stems are tender, just sauté them first before adding the leaves, to give them more cooking time.
By the way, not only is chard packed with vitamins (vitamins K, A, and C), it also is anti-inflammatory and helps the body manage blood sugar. It's in the same family as beets, spinach, and quinoa. Even more reasons to eat chard!