load-file-name is a variable which holds the full name of the file loaded by 'load'
use C-h-v load-file-name to read the documentation
Now, to load a file use the function 'load' - This looks for elisp source or binaries in the loaded paths
Eg: (load "google-c-style.el")
Note: There are another functions 'load-file'and 'load-library which work slightly differently. Read more about these here: http://www.gnu.org/software/emacs/manual/html_node/emacs/Lisp-Libraries.html#Lisp-Libraries
Also, as mentioned in one of the answers one can also use the provide - require feature.
Read this post to learn more about the differences between these functions(load, load-file, require, autoload)
http://ergoemacs.org/emacs/elisp_library_system.html