How do you use explanation in a verb?
explain is the verb.
Please explain the procedure again slowly.
"Explain this" is actually "You explain this" or some form of that phrase. As such, "You" is the [understood] subject and "explain" is action requested, i.e. the verb. Or another way of saying it is "explain" IS the verb, "explanation" is the noun, as in "You please explain the written explanation to me.' or simply "Explain it to me Lucy".
The word 'explanatory' is an adjective, a word that describes a noun. The verb form is 'explain' and the noun form is 'explanation'. Example uses: Adjective: There is an explanatory paragraph before each group of questions. Verb: You can explain to her what made you do that. Noun: That is a good explanation, I understand it now.