You can use @mentions to alert individuals to specific posts or requests for contributions. Type @ and the first few letters of their name, then select from the drop down menu.
You can only @mention people who are part of the group in which you're mentioning them (i.e. you can't @mention a colleague or contact in your network if they're not part of the group).
In Guild @mentions display the whole name.
You need to leave a space at the end of the name before you continue typing, even for punctuation. @mention links are live when they're pink - if it has gone black the @mention is not a live link and the individual won't receive a notification.