It is a slightly bitter green. There's no getting around that.
One of my favorite ways to eat it is this:
You'll need a large pot with a lid.
Saute a large, sliced, sweet onion and a few minced cloves of garlic in some olive oil. You want the onions to carmelize, so keep the heat low and give them awhile. Don't let the garlic burn.
Once the onion is very soft and browned, Throw in hot pepper flakes, to taste and stir until they are distributed and coated by the oil.
Add a large bunch of kale, carefully washed and torn into pieces. Pour in about 1/2 cup of water, turn the heat up slightly and bring to a boil, then cover it and turn the heat down so the water is barely simmering. Let the kale steam until it is tender, which can take 15 minutes or so. Stir it once or twice as it cooks down to distribute the onions, garlic and pepper flakes but do so briefly, so the pot doesn't cool off too much.
Drain when it is tender, put it back in the pot and sprinkle with balsamic vinegar to taste.
I like it mixed with mustard greens which are more bitter and slightly hot.
Another way to make it which is delicious is to toast it.
Google "toasted kale" and you will find a bunch of recipes.