How add permission to a user

Hello I work on a permission plugin. But I don’t find how to set the permissions to a player or a group.
I have made a permissions.conf with the group and user info and permissions.
But I don’t find how to applied the permissions after

You tried this?

player.getSubjectData().setPermission(contexts, permission, value)

What is context?

I recommend that you read the javadocs relating to permissions classes.