In order to transfer the files, open File Explorer from your device's menu and select the data type you want to move (photos, music, videos, docs, APKs). After that, tap and hold the file, press Move and select SD card. Alternatively, after you open the folder containing the files you want to transfer, tap the 3 dots icon, select Batch operation, check the box next to the files, press the Cut icon and paste the files to SD card.