How to install java.pkg (not unarchiver)

when i try to launch MC it says i have to have the latest java (osx yosemite) this is the day after i updated. so i download it open the dmg and then to find out that it is not a jar launcher file (btw i know where it is located and how to use jar launcher) it is a .pkg that opens with the unarchiver. i have read a previous post where it says that you need to launch it with jar launcer... i tried that but it was a fail it said it cant be opened with jar launcher and then i get a console error message. so if anyone has a solution any help would be nice.

thanks ollie.