If you have selected Arch Linux you will need to login via the console and manually configure your networking, please see: https://wiki.archlinux.org/index.php/Network_Configuration#Configure_the_IP_address for more details.
Your subnet/mask is 255.255.255.0 and your gateway is the same as your IP ending with x.x.x.1
This information was also in your VPS Server Details email.