There is two complementaries ways to search within your data collections. A full text search functionality, that you can use in addition with the categories sort functionality.
The full text search field is available from the side bar (on top of the list view before version 1.9). You can enter any string, all the cards that contains by a way or another the matching string will be displayed in the list view. Click on a list row to show and edit the corresponding card. While your search is active (a button cancel search is visible in the menu bar) you are able to navigate from the card view to the list view and vis versa, without resetting the search.
Note | « cmd F » keyboard shortcut will put the focus on the search textfield.
If your are using the categories within your collection, you can sort the list view using the sort functionality (see here). The full text search will only search within the current selected category.