Here's what each button does (moving left to right):
1. Texts
This icon takes you to your text conversations.
A notification badge appears when you have unread texts.
Tapping this button is a quick way to get to a page where you'll be able to draft new text messages.
2. Chats
Tap this to chat with other users in your account or others in your Suite.
You’ll also see a badge when you have unread chat messages.
3. Notifications
This is where you’ll find system notifications (e.g. contact import status, video encodes).
A badge will alert you to new or unread notifications.
4. Settings
Currently, the only option here is to log out of your mobile app.
More settings and customization options will be added to this area over time.