"Chats"、"Contacts"、"Discover"、"Me", at the bottom of the screen.
In this sessions, you can see the information bars containing the messages. Click one information bar, a chat box will appear and it is for users to send all kinds of messages.
The logo at the left means sending a voice message. And the two logos at the right respectively mean "emoji" and "additional functions"(like sending pictures, sights, locations and contact cards, having a video chatting and sending favorites). Back to Chats session, at the upper right corner, there is a "+".