You ice using the icer tip and smooth and you're done. I don't refrigerate my cakes unless there is fresh fruit in/on them.
Unless I'm making a chocolate cake, I do refrigerate that first, then ice with the icer tip as usual.
I'm not making another cake until Friday. When I do, I'll take pictures of using the icer tip. The only pictures I have already is for icing a cupcake cake. You may get the idea from looking at those:
OK- pretend this is a standard 9*13 (this also works with round and square cakes.
See how I am laying out the icing? It will go on thick. But don't worry. When you are smoothing it you will remove the overage. For the most part you will be able to re-use what you remove because there shouldn't be any crumbs in it.
Here you see me smoothing it with the hot knife method. With just the first swoop across, see how smooth the icing already is? This has not been crumb coated at all.
Finished cake- no crumb coating, using the icer tip, no pre-refrigeration- very smooth.
You can and should pre-refrigerate while you're learning this method. But with practice I was able to stop doing that very shortly after learning.
Round cake close up (no crumb coating and using the cake icer and hot knife)(this was one of my first cakes, so it's has some pits from air pockets in the icing- but you get the idea):
Round cake close up (no crumb coating and using the cake icer and hot knife):
Let me know if this helps or if I need to make a tutorial on Friday.