The main advantage of open source software is the broad and deep knowledge freely available on the net. On this page you will find links to pages where you can turn with questions about the modules of Recruity.
GroupOffice - crm, job vacancy management, agenda, tasks, mobile synchronization
MySQL - database management
PHP - scripting language
Kerio - mail server (or any other server, including Microsoft Exchange)

Although you can find lots of information on these sites about the components of Recruity, there are thousands of other web sites to find information and practical experiences, tips, tricks and more. Use Google (what else?)