The sections of a text are called "paragraphs". A paragraph is a collection of related sentences which focus on a single idea or thought. This single idea or thought is stated in the first sentence, which is known as the "topic sentence". The rest of the sentences in the paragraph then elaborate or explain the topic sentence.
Paragraphs can be further divided into subsections, which are known as "topic sentences". Topic sentences are short sentences which come before each new idea in the paragraph, and help to organize the text. They make it easier for readers to understand the flow of the text, and to follow the logical structure of the writer's argument.
Paragraphs can also be divided into "topic points", which are sentences which introduce the main points of the paragraph. Topic points are usually placed at the beginning or end of a paragraph, and can also help structure the text.
Finally, certain words and phrases can be used to signal transitions between ideas. These words and phrases are known as "transition words", and help readers to understand the logical connections between ideas. For example, words such as "however," "additionally," and "furthermore" signal to the reader the fact that a new idea is being added to the argument.
I hope this answer has helped you to understand what sections of a text are called. For more information on the structure of written texts, please see this link: https://owl.purdue.edu/owl/general_writing/the_writing_process/structuring_an_essay.html.