Can you please give me suggestions about how to improve this essay?
Body paragraph 1&2
3rd Rock from the Sun revolves around four main characters as they interface [Removed by Staff to protect against Internet plagiarism.]
Your biggest problems here are word usage and word omission errors. These can both be readily resolved by the use of a good online dictionary like Longman's Dictionary of Contemporary English.
Starting with "interface," this word, coined in the 1960s, is dominantly used in computer technology and thus can mislead in its usage. As a verb, it is transitive or intransitive (it may take an Object or go without an Object, either one) and is used with "with":
Longman:  [intransitive + with]: if two people or groups interface with each other, they communicate with each other and work together.
As a consequence, your sentence must read "they interface with each other about problems regarding human conditions." Here, "with" is functioning as a particle in the phrasal verb "interface with."
There is the selfish high commander Dick ...
This usage of the pronoun "there" actually converts it to the adverb "there" because your sentence only presents a long list. To correct this, your sentence must have an ending restrictive clause or an opening antecedent (plus the correct number agreement between nous and verb: is/are). Here are two examples of what is needed to correct this:
- In the cast, there are the selfish high commander Dick ..., the lieutenant ..., Tommy ..., and the transmitter ....
- There are the selfish high commander Dick ..., the lieutenant ..., Tommy ..., and the transmitter, who together comprise the cast.
all the other characters that are excellently portrayed by the actors and are realistic
You want to eliminate redundancy by eliminating "all." You want to be sure that "realistic" characters in Sci-Fi is not an inexplicable contradiction. Maybe they are realistic because they are the Earthlings?
The episode follows the story of Dick’s and Tommy’s interpersonal relationships and the problems resulting from that they deal with by emotional eating.
You want to keep track of where your sentences are going or to be careful to avoid omitting words. In this sentence, either you lost your way around "from that they" or you omitted the word "them": from them that they.
notices that he gained
Be sure you have consistent verb tense agreement throughout the essay. It is writing convention to discuss television, film, works of art and literature in the present tnese. In other word, he "follows" and comes; he "notices" and gains.
he commences on dieting, exercising and attending
This is a fine point, but the rule that applies to this usage of "commence" is described as "commence doing something," not as "commence work on something." The correct construction therefore is without "on": he commences dieting, exercising and attending.
has been, “ filling ..."
Always check commas and spacing. there are none of either needed here: has been “filling ...." The reason no comma is needed is that this is a "run-on quotation," one that completes your sentence for you.
The main characters for most of the scenes are Dick and Tommy as they both encounter relationship issues that they attempt to resolve with food.
Your paragraph-final sentence makes more sense in its summative, closing position without the distracting allusion back to all the characters: Dick and Tommy dominate the scenes as they encounter relationship issues that they attempt to resolve with food.