Within the Share an Idea area of the Community (discussion board area), you can mention people as a way of directing someone to a specific post. When you @mention people, they will receive a notification email. This is a great way of helping others make connections and be involved in the community.
To mention someone in a post, type an @ character followed by the person's name (e.g. @JohnSmith). As you type, the system will assume that you're likely mentioning someone whom you currently follow and list them first. It will then list other people whose name matches what you have started to type.
As best practice, don't mention people in a post just to get their attention. Mentions should be important and with a purpose, and unless you have a good reason to get someone's attention, this can backfire.