You will need to do both of these steps if you have a Modded Server and just vanilla if you are pure vanilla.

Vanilla

So there are two parts of giving a role depending on if you’re vanilla or modded.

ownerid <steamID> "Name" "Reason"

moderatorid <steamID> "Name" "Reason"

This will give the SteamID either AuthLevel1 (Moderator) or AuthLevel2 (Admin)

After you’ve given the needed ranks you’ll need to write your changes to your users.cfg file on the Server do that with the following command.

server.writecfg

This will write the changes to file. If you forget to do this the user will not be Admin/Moderator after the restart.

The user will need to relog to get the role if they were on the server when you gave them the role.

Oxide

If you are using Oxide / uMod you will need to grant them access via the Oxide Group

For Example:

oxide.usergroup add <steamID> admin

This will add them to the oxide group. If you wish to check what groups a user belongs to use the following command.

oxide.show user <steamID>