Poets use words to create images in the minds of their audiences. These words typically appeal to the audience's senses. Poets try to make us see, hear, feel, smell, and even taste what they are describing.
Because William Carlos Williams' poem "The Red Wheelbarrow" contains only 16 words, the poet must have chosen his words very carefully.
Two of his words explicitly conjure up images of color. The red wheelbarrow contrasts with the white chickens. We might also consider the clearness of the rainwater as belonging to this category.
Some of his words create images of texture. The material of the wheelbarrow (surely it was metal) will have a different feel than the smooth liquidity of the rain water or the feathers of the chickens.
Williams' also creates images of shape: the static roundness of the wheel contrasts with the shape of the chickens.
We might also identify images of proximity. The wheelbarrow is beside the chickens. What if the wheelbarrow or the chickens had been in a different location or position?