Haystack is using a 'tag' system to be able to group the various cards you scan so they are organized better in your app.
Each card you scan has a 'personal note' section at the bottom of it (when viewing the card in full screen).
While you can write anything in the personal notes section, you can also add 'hashtags' like #supplier, #NYC, #Buyer, #Comicon, etc.
Later on, when you want to filter your list of contacts, just use the 'search' function in Haystack's card list and search for the hashtag you're interested in - your list will filter accordingly.
Note 1: Grouping cards by company can be done by changing the list order. Tap the 'list order options button (below your own cards, but above the first card in your Haystack contacts >> select 'by company'
Note 2: Why does Haystack use tags instead of groups? We use hashtags because it is more versatile. While each contact could only belong to one group, each contact can have multiple hashtags, so it can filter into multiple groups if relevant. For example, my contact can have both a #London and a #Reseller hashtag. This means that regardless of whether I am searching for a list of contacts based in London, or a list of my Resellers, I will find the contact filed under both.