Hey - Most apps installs directly to the device's internal memory by default and not to the SD card. You can use App2SD to move some of the previously downloaded apps to your 8GB SD card (Certain apps like the Whatsapp Messenger will not let you do this) . If you are rooted (consider to do so if you are not) you can use Link2SD to move virtuall all downloaded apps to th SD card (including Whatsapp). Advice what you have and we will gladly assist further with tutorials like rooting.