The @ feature allows members to tag a specific member who will then receive a notification that they have been tagged aka 'mentioned' in that post (unless they have @mention notifications turned off). The @mentioned member can then click the notification to take them to that post.

To @mention someone simply type the @ symbol and begin typing the member name, a menu will pop up and the member you want can then be selected.

The finished "mention" will look like this: @CM-CrispMtAir and it will be a live link to the member's profile. 

Note: For the @mention to work you must select the username from the pop up menu.