Welcome to the forum. Yes, you can set the music app and camera to use the SD card, but you cannot use it as a default location for downloads. Why don't you use the phone's file manager and move your music and pictures to the card so you'll have more room on the phone?
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On my S7, the My Files app is in the Samsung folder (in Apps). There you'll see your phone storage and your SD card (at this time I don't have an SD card installed so can't go through the steps for you, sorry).