As we all know that Facebook supports tagging of friends in comments or status update via "@" like if you wanna mention/tag your friend ABC in comment then you will type @ABC and then Facebook will tag your friend in the comment, its much like Twitter where you send reply to like this.
Now going one step ahead Facebook has introduced a new way of tagging and its without using @.See screenshot below:-
It might happen that you wont see this update as it is on roll out process so if you are not getting this feature then wait a bit and you will get it soon.
Note:- You must type first letter of your friends full first name with first letter in upper case to get suggestions.