I never ate greens as a kid, my mom doesn't like them. I've learned to cook them and I like them.
One easy source of greens are the tops of some common garden root vegetables. Turnip greens, radish tops, and beet greens are all edible. The can be boiled, steamed, or sauteed. I like to use a little bit of bacon drippings to saute the greens.
I bought a bunch of beets for $1.19. We ate the root portion as a side for one meal, and the greens for another.
After washing the leaves I removed the stems. The stems are edible, but take longer to cook. After chopping the stems add some diced onion and cook the pieces in a small bit of bacon fat until they are soft. At that point add the leaves and cook until wilted.
The degree of cooking varies with taste, some like crisp greens, some like very soft greens. Stir to coat the leaves with a little fat. Season with salt and pepper. Some like a bit of sugar and or vinegar. Experiment to see what you like.