Do you mean on stable or on lazer?
On stable it's the Skins folder, and then you have to create a new folder with the skin name and put the stuff into that folder or copy another skin folder, rename the folder and edit the stuff into that folder
On lazer you have to make the skin into a .osk file and import it on the client.
If you're editing a skin you have to export the skin from lazer, extract the files (you can rename it into a .zip file), edit the files you want to edit and then repackage the folder into a .osk file (pack the folder into a .zip file and renaming the .zip to .osk) and then importing it back into lazer
Hope i explained it well