This explains what emacsclient is: http://www.emacswiki.org/emacs/EmacsClient
Basically it allows you to connect to an already running instance of emacs (which acts as the emacs "server") and opens your file in that instance. It's an alternative to running multiple instances of emacs; with emacsclient the startup time is much quicker. Some people prefer editing multiple files in emacs that way, instead of creating new buffers for the individual files. I've never seen the point and just use plain old emacs with multiple buffers.
Short version: just use plain emacs for classic text editing.