In the short story THE MASQUE OF THE RED DEATH, what does Poe use to describe the guests at the party?
I'm going to assume you mean what literary devices he uses in his description. There are several: metaphor, imagery, parallelism, and polysyndeton. Each of these serves a unique function, adding to the overall mood of wonder and increasing the suspense of the story.
A metaphor is the direct comparison of something to something else unlike it. Unlike a simile, a metaphor does not use "like" or "as" in its comparison. One metaphor Poe employs is that of the partygoers as dreams. He describes them as having "writhed in and about, taking hue from the rooms, and causing the wild music of the orchestra to seem as the echo of their steps." When the clock sounds the party stops, but when the chimes end, Poe describes how the dreams "live" again.
Imagery is language that appeals to the 5 senses. Poe uses this extensively in his stories. For example, read this excerpt about the effect of the clock on the party.
The dreams are stiff-frozen as they stand. But the echoes of the chime die away—they have endured but an instant—and a light, half-subdued laughter floats after them as they depart.
The phrase "stiff-frozen" is touch imagery. There is also a great deal of sound imagery in the words "echoes" and "light, half-subdued laughter." Even the image of of the laughter floating appeals to our senses.
The last two devices, parallelism and polysyndeton, both have to do with the sentence structure. Parallelism involves phrases or clauses that are grammatically similar, but don't contain the same words. For example, "There was much of the beautiful, much of the wanton, much of the bizarre" describes the variety in the guests' costumes. Notice the phrases that begin with "much of." Polysyndeton is a fancy word for "a lot of conjunctions." Essentially, you use it anytime you repeat a conjunction several times. In the descriptions of the guests, Poe says "There were much glare and glitter and piquancy and phantasm." The repetition of "and" allows each idea to flow into the next, and gives the reader an impression of a flurry of action.
Poe appeals to both sight and sound to graphically portray the guests in both appearance and attitude. They are extravagantly dressed, given that their host has invited them to a masquaraded ball, and they are caught up in the effervescence of the occasion. They eat, drink and dance giddily to the music, which swells and falls as waves until interrupted by the chiming of the ebony clock. At that instant, everything seems to be frozen and "on hold," but after the chiming the partying resumes its fervor.
The multi-coloured chambers enhance the orinic description of the masquerade and dancing and are portrayed as such for dramatic effect. (Some critics see them as representing different stages in life as well). They serve also as a foil for the ebony clock in the end chamber, which of course (in its ticking away and final 'gong') represents both the passing of time and the inevitability of death, which eventually is the fate of all.