SD cards don't need to be 'activated'. However, in order to download apps to your SD card (and, more importantly, to RUN them off of your SD card), you will need a rooted phone. You can take a look at this stickies that offer some methods to make use of your SD card--assuming you are rooted.
http
/www.tomsguide.com/forum/id-2327532/moving-apps-card-setting-card-default-download-location.html