I dont know how to set up admin commands for myself

You have to set the desired player as an "op".
You can do it through your server console with the "op <player>" command.
If you want to cancel someone's op status, use "deop <player]>"
Use with caution, these players can even shut down your server by default.

Is there a way to enable the operator/admin features while in Singleplayer mode?