How to put mp3s on my internal card?

I download my MP3s from my Google Drive to my tablet & they go into the Download app on my desktop, but when I try to listen to them on the default music player, they aren't found. When I have doubles of songs I already had in the music player, it asks me if I'm sure that I want to delete it from my SD card (internal); so I think it will only delete 1 but it deletes both & when I try downloading it again, it goes to my Downloads app but unable to see it on mydefault music player & when I try to find a way to put it back in the SD card, there's no way to do so. PLEASE HELP!