Start one the same way you start a one-on-one chat: select New chat  at the top of your chat list. Select the down arrow to the far right of the To field and type a name for the chat in the Group name field. Then, type the names of the people you’d like to add in the To field.

This starts a new conversation. Everyone who has access to the group chat can send messages.

You can include up to 250 people in a group chat.