I am in the process of reading up on and
learning about linux,and as i read, i am
seeing that it was built off of the unix
system platform,and i also believe that it
is used in the mac computer field,i would
like to know if this is true, and if i should
learn about the macintosh computer system as well.
a simple search for "unix + mac" on google returned ALOT of decent leads such as this one.
Linux, FreeBSD, Solaris, HP/UX, AIX, and other systems are collectively called UNIX-like systems. They all, practically speaking, conform to the standard (usually called POSIX) that is one good working definition of "UNIX-like."
(UNIX used to be a trademark that applied only to systems distributed by AT&T, but now it's part of a branding program that can be applied to any system that meets certain standards and otherwise qualifies according to the trademark owner, The Open Group.)
FreeBSD is indeed inside Mac OS X. However, it's invisible to the average Mac user. But, it's there, and more advanced users can get to it.
If you're after basic knowledge, reading up on the topic of "UNIX" will provide background for all of these systems, although not for the non-UNIX-like parts of Mac OS X. Beyond that, reading up on the specific systems you're using (e.g., Linux) make sense. For system administration, you can get even narrower, reading up on the brand-specific stuff (e.g., SuSE Linux).
Hope this helps...