Hi,
I don't know much about the LPIC certification requirements, but if you need documentation about apt-get/aptitude/dpkg and general system configuration, you can have a look at the
Debian Reference. Particularly, section 2 is about package management. The rest of the document has information on system configuration. You can also have a look at the
apt howto; it's obsolete, but I think a lot of what it's explained there still applies to apt-get.
You can find more documentation
here.
Cheers.