I general you'll need some kind of file manager. The stock samsung one (My Files) works ok for most things.
If you go into All files you'll see SD memory card and Device storage.
Choose device storage, find the content you want to move and check the box to it's left. You should then see a menu option in the top right of the screen. From this menu select move.
This should pop you back to the screen that gives you the choice of SD memory card or Device memory. Choose SD memory card.
You'll then see a list of all the folders on your memory card. open the folder you want it to go in and hit "move here" in the top right of the screen.
This should work fine for APK files, music, films, music...most things realy,
The only other thing you might have to do is create a folder for your content to go in if you've not got an existing folder you want it to go in.
To create a folder got to...
My files, SD memory card then hit the menu button (the actual off screen button) and select "Create Folder", Name it whatever you want and your good to go.