Question

what does the topic sentence of a paragraph do

Answer 1

It explains the MAIN IDEA of the paragraph. It provides a FOCUS that identifies what the paragraph will revel about the subject.

Answer 2

What is the topic sentence?
The topic sentence is the first sentence in a paragraph.
What does it do?
It introduces the main idea of the paragraph.

How do I write one?
Summarize the main idea of your paragraph. Indicate to the reader what your paragraph will be about.

Example:

There are three reasons why Canada is one of the best countries in the world. First, Canada has an excellent health care system. All Canadians have access to medical services at a reasonable price. Second, Canada has a high standard of education. Students are taught by well-trained teachers and are encouraged to continue studying at university. Finally, Canada's cities are clean and efficiently managed. Canadian cities have many p