Wow!  I must say, you really are asking excellent questions.  

Start by watching this:

Your thesis is a roadmap to your essay.  The introduction paragraph is the presentation of the thesis statement.  Then, the the essay will explain each of the points outlined in the thesis.  Finally, the conclusion will summarize the thesis and review how you proved the argument. 

When you write your thesis statement, it should have a few standard features.  It should be a declarative sentence. It should be a pretty long sentence. It should take a position.  It should explain 3 ways you will defend that position. It should make people want to read your essay.

The North and South fought the Civil War for many reasons, some of which were the same and some different. 

This statement is too general and simply rephrases the prompt. It does not answer how or why  their reasons differed.

While both sides fought the Civil War over the issue of slavery, the North fought for moral reasons while the South fought to preserve its own institutions. 

This sentence offers a more specific and debatable answer. However, it is still too broad and insupportable. You cannot defend a claim of morality in five pages, and good research would probably not lead you to this conclusion.

While both Northerners and Southerners believed they fought against tyranny and oppression, Northerners focused on the oppression of slaves while Southerners defended their own right to self-government. 

This statement is specific, clear and thoughtful. Though some might disagree with your stance, your readers will know what to expect in your paper. Now it’s up to you to defend your thesis with good evidence and persuasive writing.