To mention a group member, perform the following steps:
Open the desired group chat
Type the “@” character on the keyboard, which will bring up a list of all group members
Select the group member you wish to mention; typing additional characters will narrow the list accordingly
Use “@All” to mention all group members.
To learn how to only get notified when you are mentioned, please consult the FAQ article on notification settings for group chats (if you use an Android device) or the article on individual notification settings in iOS.