The "@" symbol is a useful and powerful feature, but use it wisely. Avoid tagging community members in every post or tagging multiple users simultaneously, as this can be disruptive.
If you want to address a specific person in your comment, type the "@" symbol followed by their username, then select their name from the list. The tagged user will receive a notification that they have been mentioned, and it will make it clear to the community who you are addressing in the thread.
Many users are not aware of this feature, but you can save time when referencing a document in your post by typing the "@" symbol followed by the name of the article or post. Select the appropriate article or post from the list, and it will appear as a linked reference.
Make sure your post is relevant to the people that you tag, otherwise you may find yourself getting reported to the moderator for inappropriate use of this feature.
Interested in learning more about marking replies as solutions? Read the How to: Accept a reply as a solution article.