Click the retweet icon to retweet:
Optionally add a comment. Click 'Retweet'.
Here's how the retweeted tweet looks:
Notice that it maintains all the original content and a LINK back to the original tweet.
That way when someone sees the retweet, they can then click through to the original, where they can then REPLY, RETWEET, or FAVORITE it.
This is the neighborly way to retweet something.