Let’s look at a passage in Charlotte’s Web:
“Fern pushed a chair out of the way and ran outdoors. The grass was wet and the earth smelled of springtime. Fern’s sneakers were sopping by the time she caught up with her father.”
Here is another way we can describe this:
There was a chair in Fern’s way. It was yellow with a colorful pillow on it. She pushed it and ran across the kitchen floor and pushed open the screen door and went outside. There was an interesting smell in the air, the kind you smell in the spring. Fern’s dirty white and black sneakers got wet as she ran toward her father. By the time she got to him, they were sopping.
One reason the second description isn’t as good is because there are too many details. These extra details take away from the action — they bog it down. E.B. White — the author — wants us to know that she is upset and therefore moves quickly through a brief description. We really don’t need to know what color the chair or Fern’s sneakers are. The beauty of reading is each reader can picture these things while following the character through her actions.