You must enter a subject or surname. The search will ignore the other criteria (topic/book/author) unless you enter a value in them. Do not bother to capitalize anything you search for. CSI ignores capital letters. For example, searching for "cox" will also find "COX" and "Cox".
Notice the different types of search for each criterion to the right of the box for your text. Make sure you are doing the type of search you need.
Click on one of the two search buttons and you will see results of the search BUT the search form will remain. The idea is that you can keep tweaking the search parameters until you get the results you want.
Be aware that using 'contains' results in the slowest searches. So try 'exact' where practicable.