Well thats ldconfig and not Idconfig.
Like kencaz said check the man pages if you want to know how to use it.
Basically you can just run ldconfig without any parameter.
Its checks the library path inside /etc/ld.so.conf and the libraries inside /usr/lib & /lib and caches them. You must run it after you've installed new library files so that they can be linked. Most of the program installation scripts do that for you automatically.