The Results Matrix shows you the number of times each card was sorted into your pre-set categories in a closed card sort. The darker the blue, the more often the card was sorted into that category.
You won't see the Results Matrix if you've run an open card sort because you don't give participants any pre-set categories. Instead, you'll see the Dendrogram, the Similarity Matrix, and the Participant-Centric Analysis.
You can view this matrix from different perspectives, depending on what you're most interested in and the results themselves.
You can go by color as a quick reference — the darker the blue, the higher the percentage of participants who placed the card in that category. So you can quickly see if one category was by far and away the most popular, or if there is more of a distribution across the categories (and therefore less agreement between participants).
You see the number of participants, though, not the percentage, so keep in mind how many participants you have altogether so you can reference it in your analysis.
Looking at the data by card
If you're running a closed card sort with your pre-set, top-level website categories, one of your primary questions will be 'Where do most people think this information belongs?' So looking at the cards one at a time will be a useful thing to do.
When one category is by far the most popular for that card
When a card is placed in one category significantly more than any other, you can be confident that the information should be in that category on your actual website. For example, here we can see that out of 49 participants, a convincing 44 placed the card 'Pay my bill online' into the category 'Account':
When one category is the most popular, but others are quite popular too
When a card is placed in one category more than others, but still appears at least 5 times in any other category, your decision about where to include the information on your actual website will be less straightforward. It will be up to you what your number thresholds are.
In this example, we can see that the card '3G coverage map' appears in the category 'Services' 18 times out of the 49 completed card sorts. And though it is 5 more than any other category, it only works out to around 37% of participants — which of course means that around 63% of participants disagree with that placement.
We can also see that 11 participants placed the same card in the category 'Internet Services', and 13 placed the card in the category 'Bananacom'. So you could look at all three most popular categories and decide if they're as distinct from each other as you had thought (we could merge the two categories 'Internet Services' and 'Services', for example).
When no category is any more popular than others for that card
Sometimes you'll see a card row that contains numbers in every column and not much blue shading. When you see this, there's not much agreement between your participants about where the information belongs.
It may be that the card label is quite general, and could logically belong in many of the categories. Or that the card is ambiguous, and so people had to guess about where it belonged. It will be up to you to establish why this might be.