There are differences in sharing. Posting stuff other people have made to Steemit is fine. When you share something you haven't made, you're getting rewarded for sharing it, not for the content itself.

But:

• Don't copy and paste entire articles or writings. Selectively quote an article and link to its original URL.

• If it's a photograph or picture don't let people assume it's yours by giving attribution (as best you can) or at least saying it's not yours.

• Posting youtube videos is generally ok because it's usually obvious it wasn't you who created it. Of course if you did make it, say so!

Original content and shared content can coexist on Steemit as long as it's clear who originally created it.