When you're trying hard, or working hard, you're putting in effort, and you're making an effort to do something. Effort is the hard work that it takes to get something done.
It takes a lot of effort to learn a new language, but your effort pays off when you get to talk with new friends in your new language. It takes a lot of effort to plant a garden and take care of it—but when your flowers bloom and your vegetables mature, it's wonderful to see your effort pay off.
It takes a lot of effort to bake beautiful cupcakes. Baking cupcakes is effortful. But it takes very little effort to eat a cupcake! Eating a cupcake is effortless.