What is a security patch and what is a patch manager? :)

A patch (in computer talk) is a correction for a program. Corrections usually are written to fix bugs in the program. Another type of patches is meant to immunize the computer for virus/trojan attacks. These patches are called "security" patches (they "close" "open" doors, through which a virus/trojan could infect your computer).
A patch manager is a program that automizes the updating of the computer to the latest patch level, including searching, downloading and installing patches.
It is a good idea to install at least all available "security" patches.