To create a group of IP addresses, select the 'show sidebar' button on the top menu. Under 'Resources' select 'Security'. If you have already created IP address groups you will need to click 'Manage Security'. From here click 'Create an IP group'.
Provide a name to your group and the list of IP adresses you want to group and click 'Create'. After creation, you will either be able to edit or remove the group you have just created.