Once in the Serials module there is basic search box at the top that you can use to find subscriptions using any part of the ISSN and/or title.

You can also click the 'Advanced Search' link to the right of the 'Submit' button to do a more thorough search of your serials.

From your results you can filter by using the search boxes at the bottom of each column and adjust the number of resutls using the toolbar at the top of the results set.