There are a few ways to go about finding books on presidential decision-making during wartime (or peace).
First, you can try out several keywords, generally involving the war and the associated president. For example:
These searches will only show results that contain ALL of the words that you typed in. This is why I only searched the last name of the president. If I included Woodrow, it would exclude all sources that did not have the name Woodrow. So, start with just the last name. You might also want to try a few different ways to spell the war in question. For example:
This, however, will likely give you very broad results. You will want to use the vocabulary you've been gaining from your work in the course to add some additional keywords to get a more specific focus. For example:
After this, you will look under "Type" on the left side, and click on both Print Books And eBooks.
To learn more information about a book, click on the book's title and review the full record. If you scroll down to the Details box, you can read a summary of the book, and also look to see who published it (try to focus on University or College presses; if it is not, please verify with your instructor).
Subject headings are like hashtags applied to sources that categorize them under a specific topic. They are not perfect, and you will not find everything on that topic by just clicking on one subject heading. But, if you are struggling to find additional books, this is helpful. Once you find one great book, scroll down to the Details field and look under Subjects. You can click on any of these words, which will lead you to a list of results that are categorized under this subject heading. For example (example below), clicking on World War, 1914-1918 will bring you to all materials with that tag. As you can see, this is an odd subject heading for WWI - which is why it is good to start from a source you already found.