1. Navigate to Settings -> Wireless & Networks -> VPN
2. Click the plus icon to add an additional VPN profile
3. Enter a VPN name for the connection.
4. For the Type drop-down, select L2TP/IPSEC PSK VPN
5. Enter the public IP (found in Dashboard under Security appliance -> Monitor -> Appliance status -> Uplink) of the MX device under Server address.
6. Enter the pre-shared key under IPSec pre-shared key. Hit Save.
You will be prompted for credentials when you connect.