You can set up your queries by just entering a serch term and choosing a search field from a menu. Combination of search terms via boolean operators is realized through mouse driven menus as well.
Additionally you can check each query immediately at NCBI's Entrez. This will present you with some sample results and give you a feeling on how to further specify the query.
Once all queries are set up, click on 'Submit' again until you arrive at a site where you can either choose to see your configuration file with the default PubCrawler options or modify these options first.
The resulting configuration file can be saved on your local harddrive and used for your next PubCrawler run (always use the 'Check'-option after any changes made to the configuration file).