You will need to keep a record of your sources so that you can include them in your bibliography. So when you find useful information which you might use, write down the name of the book or journal, the edition, page number, author, date of publication and publisher.
Planning your essay involves organizing your ideas into a logical order. You can do this by creating a mind map or by making a list of headings with bullet points under each. Your essay needs to be well structured. You will need to write an introduction which explains what you are writing about, introduces your central idea and the point of view you plan to support. Then you will go through each of the relevant points, linking them in a way that flows and makes sense of the topic.