You can use the service without registering as a member.
*See here on how to start using it on each device
However, we recommend registering an account in order to transfer your data to a new device in case you ever lose a device or change the device that you are using.
How to register
Tap the menu icon at the bottom of the screen
Tap "Settings" > "Account"
Go through account registration via "Login method setup" at the bottom by one of three methods: (1) Facebook Connect, (2) Twitter Connect, or (3) Enter email address/password