Answer:
1) Authors try to persuade by trying to convince you to do something. For example, they could be trying to persuade you to buy something by listing all the positive effects of that item and how it could help.
2) The central claim is basically the authors main idea or main argument so most likely, the whole passage will be about it but you can also find it in the first paragraph (introduction paragraph)
3) "a rhetorical device, persuasive device, or stylistic device is a technique that an author or speaker uses to convey to the listener or reader a meaning with the goal of persuading them towards considering a topic from a perspective, using language designed to encourage or provoke an emotional display of a given perspective or action. Rhetorical devices evoke an emotional response in the audience through use of language, but that is not their primary purpose."
Hope this helps