Nagios Support Forum

Where can I find detailed description of how does Nagios read, collect and handle at all information?

I would start here, but note you won't find answers to all the items you mentioned in just one article:
https://assets.nagios.com/downloads/nag ... n/toc.html

These particular articles may be of interest:
- Configuration Overview
- Object Configuration Overview
- Object Definitions
- and then anything under the basics section

There's a lot to cover, bur definitely let us know if there are any questions, thanks.