This is probably one of the most perplexing concepts for new writers: what is "show" and what is "tell"? And how do you balance the two?
I think someone once said: "Action is story."
"Show vs. tell" basically means: don't tell me he's angry, show me. Don't tell me he's sad, show me. Don't tell me she's beautiful, show me. Don't tell me Hurrican Katrina is devastating, show me.
Of course, there are times when you just have to tell. To know when to show or to tell is the art of writing stories. To strike a good balance is mastery.
The key here is to pull the readers into your story, and keep them there. Show vs. tell is merely a tool to do just that.
It doesn't matter how wonderful your prose is, if you can't keep your readers in that dream state -- that dream world of yours -- then you're not do a good job.
Show is always more interesting and evocative than tell.
Tell is always more direct, straightforward and quicker.