adverb

today i learn adverb lesson.

today is easy.
but i don't understand about preposition.
maybe nuance.

industrious is personality adverb.
industrial is business adverb.
interest and interesting are noun.

i can't understand the different between "he is in the park" and "he is at the park".
may be in the park is inside.
at the park allowed around the park.

i am here to by some stuff.

stuff means material.