Well, you will need to be running at least, or able to update to, Android "Marshmallow". Then you will also need to have a device that the manufacturer hasn't restricted this option on. Which does happen, a lot. Below are the instructions on how to make the change. If you have the right Android version(s) as listed yet the instructions don't work for you, or some of the steps are missing on your device, then the manufacturer has restricted the option on your device.
NOTE: This is if you are wanting to move and run apps from the card. Now if you just want to move photos, videos, music, etc., and not apps, you just need to change the location within the app you are using for those files.
How to turn the "External" SD card into...