Posting @replies and mentions
Type your comment as you normally would, but replace any names you include with that person's @username. For example:
Hello @Michael
Posting Youtube Videos
Just enter url of a video and click Comment.
Example:Checkout this really cool video:
http://www.youtube.com/watch?v=4kpHmtA7LOk
Using Hashtags
People use the hashtag symbol # before a relevant keyword or phrase (no spaces) in their comments to categorize those comments and help them show more easily in Search.
Best practices recommend using no more than 2 hashtags per comment.
Example: Don't spam with #hashtags