These are categories that help you organize the entries in your address book. For example you can group your customers by industry sector or by year of first sale or ......
You will see a link to the CRM search page in the Address-Menu
Before using you should create the groups. After creation you will have a select box whenever you create or modify an address or company or department. With this selectbox it is possibly to add the address entry to one or more CRMN Groups.
Looking at a address or company entry will show you all CRM Groups of this entry.
Looking on a CRM deatil page will show you all members of that group.
Simply visit the modify dialog in order to move a address entry to another (or no) CRM Group.