i open the installer and i go through the steps and when i pick the USB Flash Drive it says " OS X Cant Be Installed On this Drive: OS X Is Not Installed"
MacBook Pro 15″, OS X 10.11
The USB Flash Drive as the destination for the Installation of What ?
Installing a version of macOS or OS X in a USB Flash Drive will never work as well or at all as installing it onto the Internal Drive of the computer
If the user is attempting to make a USB Installer on the USB Flash Drive that is a different matter.
To perform this action will require booting from a Bootable Installer.
EDITED
The USB Flash Drive as the destination for the Installation of What ?
Installing a version of macOS or OS X in a USB Flash Drive will never work as well or at all as installing it onto the Internal Drive of the computer
If the user is attempting to make a USB Installer on the USB Flash Drive that is a different matter.
To perform this action will require booting from a Bootable Installer.
EDITED
It sounds like you downloaded a macOS patch. A macOS patch requires a certain version of macOS to be installed in order to "patch" that OS. The full macOS installers can be downloaded from the link provided by @P.Phillips.
when i open the installer and pick the usb drive it says OS X is not installed
