There is so called "Install Package Files" on the game category on your PS3's XMB. If you dont have that one then your PS3 is simply not jailbroken, at least on most CFW available today but only some of few CFW today doesn't have a "Install Package Files" and "app_home" on their XMB but there will be a some sort of toolbox there that can still function as pkg installer still only useable in CFW PS3's.
It should be displayed in both CFW & OFW, you can find it in the Music or Video category on the XMB(XrossMediaBar) in case you need to play music or install themes create a folder on the root of your USB & rename it to PS3 & then folders for the files you need to play or install:
THEME for themes
VIDEO for videos
PICTURE for images
MUSIC for music & so on, all folders must be in CAP
as for the .PKG files just put them on the root of your USB.