I'm new to this and just want to know when using a cake leveler if the cake should be warm still or cooled off?

Warm is o.k. but not hot out of the oven
Let it cool in the pan about 10 minutes on a rack, turn out & let cool another 10-20 minutes. You can then level and allow it to completely cool.....wrapped in plastic.
One can also level a cold cake. I have found I have problems if it is fzn but cold (like out of the frig) is fine.
Either way is o.k.