The search facility is currently pretty simple: it searches for an exact match of what you type and doesn't have a great deal of "intelligence". For instance, you could search on the word "the" and retrieve quite a lot of records (most search systems weed out words like this). It does search for references in both the title and the description of each item so you can, for instance, type the name of an artist whose cards you are interested in. This information is unlikely to be in the title, but may well be in the description of the item and the search facility should be able to find it for you. However, be sure to read the notes in the next paragraph for a warning!
If your type "playing cards" it will find every instance of the two words with one space between them (on this site quite a number of results!) If you type "playing crads" (i.e. cards mispelt) it will report no results. Many search functions might look for both the word playing and the word cards and report anything with EITHER word. The search function on this site will only find instances where ALL words you type are present AND immediately adjacent in the order you give and spaced precisely as in the catalogue. Limiting though this might be, it does have its uses if you want to find something specific. If you were looking for items relating to Beatrix Potter, you could type just Potter and get the Beatrix Potter items lumped together with anything else which might have Potter in the title or content of the catalogue entry. To exclude Harry Potter items etc, type Beatrix Potter and you will get just the Beatrix Potter items.
You can type as many words as you like, but given the constraints explained above, typing lots of words will drastically reduce your chances of finding anything rather than widening the search.
You may limit the search by selecting any of the sub-catalogues from the dropdown box.