For your pictures, videos, documents, music: use a file browser app to COPY the files to the SD card. After you are sure all the files correctly made the move, then you can go back and delete the files from the internal storage.
For the apps: you don't move them. They stay on the internal storage. Yes, sometimes you can move small PARTS of them to the SD card, but it is not worth the effort and causes more problems than you think it solves in many cases.