As you type, sample results will appear so you know if you need to further refine your search. When you've got an alert you're happy with, choose Show Options. Here you can choose how often your alerts appear, and whether you want to see all the results to your query, or only the most relevant. The latter option takes into account several factors, including the site it was published on, and how many times people click on it, among others. This option is much more helpful if you're looking for something that returns a lot of hits.