Should I refer to a tutorial as a how-to or a how to? Is there a grammatical rule for this?
That is how it is to be written, as you mean a certain thing (the way) defined by the phrase. Without a hyphen it would not refer to the specific thing but just be a phrase.
"The how-to of it all is explained in this tutorial."
"This tutorial shows how to do it all."
There is a distinct difference.