Well, the person who's Twitter account it is, is the one who makes the actual posts to their Twitter page.I'm not a twitterer (tweeter?). How does it work?
If the person writes something like @cnnpoliticsnews (for instance) that sends a special alert to that person or account holder. And, it is of course posted to the account page of the Twitterer.
If the person posts something like RT @lrflw @joanwalsh Barry Bonds wins big victory in 9th Circuit; feds cannot use +urine evidence for perjury||He was a scapegoat, so sad
That means, they are RE-Tweeting what someone else posted.
If someone posts something like: At Glenmorangie, they call the still room "the cathedral." #whiskeytheology
The #whiskeytheology is a way to categorize and also in the case of some writers to editorialize. It acts as a tag. If you click on it, Twitter will search for all posts that use that 'tag'.
Hope that helps.