Welcome to Android Central. You can use the file manager that came on your phone, but I would suggest first using your photo app and see it that will copy them over as it will create the folder structure for you. I would also strongly suggest first backing up everything to a cloud account, then do a copy, verify all the files you copied are on the SD, then delete those from your internal storage. SD cards fail fairly often, many with no warning, so back up everything of value somewhere else.
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