A modifier is a word, phrase, or clause which functions as an adjective or an adverb to describe a word or make its meaning more specific.
Here is a link that explains and gives examples.
Specifiers are shown as being of three kinds: Qualifiers, Determiners (like a, the, this, that, these, their, its, those, my, his, her, your and proper-noun possessives), and Degree Words (like too, so, very, more, most, quite).
So Modifiers enhance a noun and Specifiers give possession, quantity and resemblance to a noun
I hope that helps and good luck on the exam.