If you open a book, you will notice groups of words. These groups are called paragraphs. I will show you an example.
This is an a paragraph. It is the second paragraph in this answer. Notice how there is a space before the first word in a paragraph. This is to show the reader where the paragraph begins.
The reader can tell that a paragraph has ended when a new one has begun. This is the third paragraph I have written here.
Authors and writers use paragraphs to organize their ideas. Each paragraph has one main focus. Paragraphs can have any number of sentences, as long as all of the sentences in a paragraph are about the same thing. If I wanted to talk about rabbits right now, I would need to make a new paragraph, because rabbits have nothing to do with what this paragraph is about.
A topic sentence is how you start your paragraph. The reader knows what the paragraph is going to be about by reading the first sentence, which is the topic sentence. You knew that this paragraph would be about topic sentences, because that's what the first sentence in this paragraph was talking about.
For your homework, you are going to want to think about the question: Why is it important to treat people fairly in school? A good idea would be to write down a list of reasons why you think it's important to treat people fairly in school.
After you've done this, choose what you think is the most important reason, and create a topic sentence by restating the question, followed by your reason. Example: "Treating people fairly in school is important because...(your reason goes here.)"
Your examples could be about what you think might happen if people are not treated fairly in school, and why it would be bad. Example: People will be sad if they are not treated fairly in school. They will be sad because people don't make friends when they are not treating others with kindness and respect. Having no friends makes people lonely and sad.
I hope this helps! Good luck!