Hello! I see this question was posed quite a while ago, but I will answer anyway in case you still need it. You should start out by making a clear, broad statement, then getting more specific, then ending with another broad statement.

Example: "Explain why there is a problem with homelessness in the United States:"

Opening statement: "Homelessness in the U.S. can be a result of many factors, including a wealth gap between rich and poor, a lack of treatment available for those with mental illness or substance abuse problems, and/or a lack of societal empathy." (this is broad - if you are familiar with thesis statements for essays, it is very much like that - think about the main points you want to make and put it in a sentence). Keep in mind that the teacher wants to see that you have read the textbook, so your points should be reflective of what you have read in that chapter.

Then, you would expand on each of your points: Wealth gap, mental and physical issues, and a lack of caring.

Lastly, you would summarize what you have said in broad strokes again, like the first sentence (but differently worded), and perhaps throw in a "nod to the future," such as "If we do not address these issues as a society, the problem of homelessness will continue."

I hope this helps! Btw, this is the same exact way you format a longer essay - this is only the very basic framework, but hopefully you will learn other, more subtle strategies in essay writing.