In Bridge you can either tag files or rename them. I just use the renaming, as many of the items come from the designer already named. I also use Name Mangler to help with the renaming business on a batch basis (good for getting the names consistent).
To rename a file in Bridge, just click once on the file to highlight it, then again on the name to highlight that, and change it. To tag a file in Bridge, you use Keywords. There's a Keyword panel that you add to your workspace view (see the Window menu). Once in the Keywords panel, you can see there are some categories that are defaults (Events--Birthday, Graduation, Wedding), etc. that you can use to tag your photos. So, first you need to add the various keywords you want to use, then assign them to the files. For example, you might want to tag scrap supplies with a general name like flower, then a color in addition (separate keywords).
Thereafter you can search through a whole designer's stash with one query, which is done from the "Find" located under the arrow at the top of the Keywords Panel. Or even look within a particular store site, such as GDS, for any element matching your query among all the designers at a particular store. That is only, of course, if you've set up your organization system in that particular way: Store--Designer--Kits. If your system is different, you will search differently. If you've got designers who sell in multiple stores, you might then have to add the designer's name to the keyword search.
The renaming scheme (which I use) has the additional advantage of being Finder-friendly; you can search for things in the Finder (Mac specific technique here) without needing Bridge open. If you've got the Finder showing the icons in list view, you will even be able to see a little preview in the Find results screen.
Hope this helps, Maggie. Do whatever suits your organization scheme and is easiest for you.