The @mention functionality allows you to link a person, place or piece of content in the community. This functionality can be used in when collaborating.
When @mentioning a person the user is sent a social interaction notification in their Inbox. Depending on their preferences they will also get an email about. Tip: @mentioning someone in content they are already participating will generate 2 notifications, one for the @mention the other for the update to the content.
When @mentioning a place it will be noted in the place's activity stream and therefore all members/followers of a @mentioned place will see that activity in the Stream they have chosen for that place.
Alex is referring to this community, not SugarCRM.
Francesca Shiekh is correct. This document is posted in the Getting Started space in the community which is where documentation about how to use the community is stored.
Is there feature like this in sugarcrm? I know salesforce has chatter.
You can reference Users and Records in Activity Stream.