Show, Don’t Tell. It’s the first law of writing.
Show: Joe knew we were hungry. He treated each of us to dinner.
Tell: Joe was generous.
But you do need some telling. You might start your story with the heroine falling out of an airplane (showing), but you have to tell the reader how she got there and why she’s falling. Experts say that in creative fiction the ratio is about 80% showing and 20% telling.
Mariska Stamenkovic gives us a good example:
Suppose I want to convince you that my neighbor is a slut. I could tell you:
“She has no morals at all, I’m telling you. She’s as ethical as a doornail. Really. Believe me.”
Or I could show you:
I take you by the hand and lead you to the park across the road. I push aside some branches and point. There she is, my neighbor. Bare-ass nekkid on a park bench, making out with three guys, none of them her husband.
Which approach is the more convincing?