Answer:
they stress how positively Miss Brill views everyone at the park
We know it is iambic because we are able to stress every other syllable.
Just a little hint: Not all, but most poems are written in iambic. Even a lot of pop songs now-a-days are written in iambic meter ;)
I believe Shakespeare had about 150 sonnets and only a few were not written in iambic. Crazy.
