If you want to add a new search directory for require you would do so for .lua files with package.path, with package.cpath for .so or .dll files (shared libraries that export a luaopen_*() function).
I frequently do this in a project if I'm requiring in a .lua from the same directory:
package.path = './.lua;' .. package.path
require 'local_file'
Look at package.path, it search those directories for the file you're require'ing in from left-to-right -- all the directories are between ; (; is the separator)
Remember: package.path for .lua -- package.cpath for .so/.dll
