When you purchase new devices, you will receive an email with instructions on how to activate your new devices.
Visit www.samsara.com/activate, create an account and follow the instructions online.
Once logged in, your devices will activate, and you will be redirected to the settings page in your account.
Existing customers can activate new devices by navigating in the Cloud Dashboard to Settings > Gateways > Activate Devices and entering using the serial number located on the back of a device.
To name the gateway, follow the instructions found here: Name a Gateway