Type in your message where it reads "Enter your message here", below the chat messages. You can send you message by pressing Enter or clicking the "Send" button. For line break, press Shift+Enter.
Click the "To" button, and select someone in the group chat. You can also search for someone too. If you want to select multiple people, push the Shift key and select.
In the message field, it will automatically show up as "To: *******", but everyone in the group chat can see the message.
Edit your message
Click the pencil icon that shows up when you hover your mouse on a message that you want to edit. The timestamp will automatically show up on messages being edited.
Delete a message
Click the trash icon that shows up when you hover your mouse on a message that you want to delete. Confirm the warning text, and click delete. Please keep in mind that you will not be able to retrieve your message once deleted.