Explain what you're trying to do and I'll be able to help. Anyways, here's how you would call a graphic from the cache.
RPG::Cache.cache_type(file name, picture hue)
cache_type is what folder you're trying to pull a graphic from.
file name is the name of the graphic you're trying to use.
picture hue is the hue of the graphic.
I.E If you want to use a battler, it'd be RPG::Cache.battler(file name, picture hue)