I go to the server, I write / skin and writes to me that there are no rights. How to issue them I can not understand

Open plugin description, I listed there all permissions. Open oxide documentation (umod), we listed there commands for permission system.

What needs to be done to register after oxide.grant name and what "permission"?

Please, learn how to use oxide - it's not related to my plugin, sorry, cannot help you.
https://umod.org/documentation/plugins/permissions