Samsung Galaxy Core users get only 8GB of flash storage, out of which only 4GB is available to the user. While you can use micro SD card to expand storage, only internal storage is used for storing apps. Here is a guide on how make everything store on external micro SD card.
1. First root your Samsung Galaxy Core by following step by step instructions from here.
2. Now, download external2internal app from Play store.
3. Start external2internal app and grant it root access. Tick send rescan and use per default options.
4. Then press Original Mounting Point And Change To ‘storage/sdcard0’.
5. Now, select original External Mounting Point And Change To ‘storage/ExtSdCard’.
6. Tap Ext.Sdcard Device Access and Change The Value From 179:49 to 179:33.
7. Now press back button and tick, At Boot Option and select External>Internal.
8. Wait for some time and reboot your Samsung Galaxy Core.
If still no success, go to external2internal app again Press External>Internal.