Copy the files and folders for the wanted nemo action to your nemo actions directory. Linux Mint stores the Nemo Actions in ~/.local/share/nemo/actions (user) and /usr/share/nemo/actions (system-wide).
Also make sure the shell scripts (if any) are executable.
Your Nemo Action will appear in the context menu when you right-click. Actions on files will appear only if right-click-ed file is of supported type (e.g. mp3). If you don't see the Nemo Action, log out and back in.