This poem can be very confusing. With all difficult poems, we have to consider what might be suggested by symbols, images, odd words or phrases, and that such a poem might be interpreted in different ways.
First, think of the title. It is odd to consider an emperor of ice-cream. Emperors tend to be very powerful people, in charge of whole nations. An emperor of ice-cream sounds like character in a children's story or maybe the one who inspects ice-cream to make sure it's the best quality. In this poem, Stephens is placing the emphasis of importance on ice-cream. Ice-cream is such a nice treat in life, surely it is worthy of an emperor. In fact, the line is repeated at the end of each stanza: "The only emperor is the emperor of ice-cream." This implies that there are no other important emperors, rulers, kings, and so on. Stephens insists that it is the small, intimate, daily pleasures in life that are important; not some notion of greatness that exists in some structure of hierarchy or authority of a governing emperor. What is important is what is real and graspable; things like ice-cream.
In the first stanza, the speaker demands that someone call in the muscular man, strong apparently from rolling cigars. He is summoned to "whip / Into kitchen cups concupiscent curds." He typically roles cigars which tend to be smoked in celebrations. So, they are calling in a guy associated with parties. He is summoned to whip up concupiscent (involving sexual desire) curds. What kinds of curds might elicit desire? The answer may be ice-cream. While ice-cream might not be a sexual desire to some, Stephens is playing with the idea of desire. We are driven by different urges of desire; the desire for sweets is one of them. This is part of one underlying theme of the poem; enjoy the good things in life, like ice-cream.
The women are not wearing anything special and the boys have not really gone to any real trouble with the flowers, having wrapped them in old newspapers: no bows, no extra effort here. The speaker adds, "Let be be the finale of seem." That is to say, let being (what we see, life itself) be the finale (end result) of what we seem to see. The speaker means that what you see is what you get. Another interpretation of this is that appearances (what seems) are not as important as what is (what is being: be). The lack of effort on the part of the wenches and the boys suggests that they are going through the motions. And even though they are at a solemn event (which becomes somewhat clear in the second stanza), the speaker suggests that because they "seem" to lack a lively spirit, that is actually who they are "being." A possible implication is that if they want to be happy or hopeful, they should act (seem) that way.
In the second stanza, the speaker demands that someone take the embroidery of some (recently deceased) woman from her cheap ("deal" implies cheap wood), dresser and cover her face with it. The covering of her face implies that she has died and that this is a funeral or a wake. If her used up feet ("horny" meaning that they show physical use: callouses, etc.) stick out, it is to emphasize that she is dead: "cold" and "dumb (mute/silent). The next to last line suggests that we (or those at the funeral) should shed light on something: the idea that the only emperor is the emperor of ice-cream. This idea, juxtaposed to images of people attempting and/or failing to show signs of life (cigars, making ice-cream) in spite of the sadness of the event, brings home the point of the poem. And that is to enjoy the good things in life. A reminder that we all will die some day is depressing, but not if it is used to inspire us to make the most of the time we have; whether that is by eating ice-cream, celebrating other small things in life, or by celebrating the life of a recently deceased friend/family member.
Eating ice-cream is also a temporary thing; it doesn't last very long. On a larger scale, the same is true of life. Therefore, we should enjoy each because to greater or lesser degrees, each is fleeting.