Just fill in as many fields as possible and click Start Search button. You don't need to complete every field to begin searching, but filling in more fields will give you better search results.
The last name of the composer and part of the composition title are usually enough information, such as the composer name and the instrument. Use the LAST name for composer and if you don't know how to spell the entire name, try the first few letters.
With the field "Release Date" you can narrow your search to items added to our catalog since a given date.