Imagery is the use of the five senses to describe and recreate the actual sensory experience of the moment itself. There is a lot of imagery in the poem-too much to actually give all of the examples, but here are a few: "blue towel" "damp weight of hair" "dripping water" "sun-warm clothes at twilight" "the strain of threads" "swollen magnolias" "shadow of moths". All of these are descriptions of the sights, sounds, tastes, touches and smells that she felt while sitting on the porch.
Figurative language can come in various different forms, but one technique is a simile, where you compare two things using the words like or as. She says her hair's weight is "bulky as a sleeping cat," and the afternoon's length "like the stretch of lawn spread before me." She compares the flowers to being "heavy as a flock of birds in the tree," and her hair was "like a measure of wealth, like a bridal veil". So, she uses quite a few similes to bring her message across and give a sense of elegance to her poem.
I hope that those examples help; good luck!