“Decline I” is an instruction for the student to provide the first person pronoun in all cases: I (nominative), me (accusative/dative/ablative), my (genitive), mine (genitive substantive). (I have borrowed the case names from Latin, with which I am more familiar. I think the English cases are nominative, objective, possessive.)

I believe the misspellings in the spelling section are intentional so that the student will identify them—I am guessing that’s the point.