Adjectives are words that modify (describe) nouns. This means that adjectives are extremely common in most kinds of writing, including poetry. "I Stood Tip-Toe Upon a Little Hill" is full of adjectives. Consider the first two lines of the poem:
"I stood tip-toe upon a little hill, / The air was cooling, and so very still..."
The bolded words are adjectives. Why? Because "little" describes the hill, and "still" describes the air.
Think about the next few lines, which get a little more complicated:
"That the sweet buds which with a modest pride / Pull droopingly, in slanting curve aside..."
Again, the adjectives are bolded: "sweet" describes the buds, "modest" describes the pride, and "slanting" describes the kind of curve that the buds follow. "Droopingly" is an adverb, meaning that it describes a verb ("pull") in the same way that adjectives describe nouns.