I forgot to include the following sentences. Thank you very much.

1) The story is mainly set at night.
The setting in time of the story is the night (is this possible?)
2) Another important theme is that of fear.
3) Dr. Frankenstein challanges the laws of nature as soon as he creates a human being by joining together selected corpses.
4) Your paragraphs contain a lot of grammar and spelling mistakes as well as repetitions.

1. The setting of the story is at nighttime.

OR
The story occurs at night.

2. Fear is not a theme. It is an emotion and can be a mood, though. Look here for ideas for themes:
http://www.sparknotes.com/lit/frankenstein/themes.html

3. OK

4. ... repetition.
(or redundancy)

No problem! I'll address each of the sentences you provided:

1) The story is mainly set at night.
To determine if this statement is possible, we can examine the text or analyze the story's descriptions and events. Look for clues, such as specific mentions of nighttime or darkness, actions that commonly occur during the night, or the overall mood and atmosphere conveyed by the author. By doing this, you can gather evidence to support or refute the claim that the story is mainly set at night.

2) Another important theme is that of fear.
To identify themes in a piece of literature, you should closely read and analyze the story as a whole. Look for patterns, recurring ideas, character conflicts, or symbols that relate to fear. Consider how fear is portrayed, the impact it has on characters or events, and any messages or lessons the author may be conveying about fear through the story. Additionally, examining critical analyses or scholarly interpretations about the text can provide further insights into the themes present.

3) Dr. Frankenstein challenges the laws of nature as soon as he creates a human being by joining together selected corpses.
This statement describes an event in the story, which can be verified by reading the relevant sections. Find passages or chapters where Dr. Frankenstein creates or assembles the human being using selected corpses. Pay attention to the explicit actions, dialogue, or inner thoughts of the character to determine how he challenges the laws of nature according to the story's context. By analyzing these textual references, you can confirm the accuracy of the claim.

4) Your paragraphs contain a lot of grammar and spelling mistakes as well as repetitions.
To identify grammar and spelling mistakes, as well as repetitions, it is best to carefully read through the paragraphs and proofread them. Look for errors in grammar, such as subject-verb agreement, incorrect word usage, sentence structure, or punctuation mistakes. Additionally, pay attention to repetitive phrases or ideas that may need rephrasing or consolidation. Utilizing proofreading tools, like grammar checkers or online writing assistance platforms, can also help identify and correct these errors to improve the clarity and coherence of the paragraphs.