If you want to install an app in SD CARD directly via APK, then download the APK file of that app via KIES software (automatically downloaded in APK format). This APK file will be saved in mobile, copy that APK file to computer, and install the same as per the above video. You can also download APK file from Google Play Store directly on computer.
This video is a guide to install APK (Android Package Files) files directly to SD Card/USB Storage. If you want the guidance to install Java JDK, Android SDK and connecting Android device to ADB utility, then you will need to watch my earlier uploaded video http://youtu.be/CVOj2WnEeLw
I have tried my best to give you step by step instructions. However please do it at your own risk. I shall not be responsible in any means or manner.
Please note that DOWNLOADING APK FILES from GOOGLE PLAY is against the terms of Google Play Store.