I just read a bit more and I think this is what I need
The Keywords panel in Bridge is for storing and re-using keywords to apply to other images. If you wish to transfer the keywords from your files to the Keywords panel, there are a couple of methods:
1) Export the keywords from your files to a text file and then import the text file so that the Keywords panel has a persistent list of entries, that you can put into groups/categories.
My comment: I tried this but the only Keywords in this text file were the ones from photos I had already clicked on. Do I really have to click on every photo and then make them 'persistent' or is there an easier way? I think this is what #2 below describes. Just very time consuming to have to click on every photo.
2) Browse your images so that the keywords in the files that do not exist in the Keywords panel show up in italics under the "other keywords" category, then right-click each of them and make them "persistent", that you can put into groups/categories.
https://helpx.adobe.com/au/bridge/using/keywords-adobe-bridge.html
Either way, you need to decide if you are going to use a simple "flat" keyword structure, a Parent/Child keyword structure or a Hierarchical keyword structure.
https://helpx.adobe.com/bridge/kb/nested-hierarchal-keywording-bridge.html
Something to understand:
You can keep a list of keywords within Bridge. These keywords may or may not have been applied to photos.
If a keyword has been applied to a particular photo, then when you select that photo the box to the left of the keyword will be checked.
If the keyword has not been applied then you may check the box yourself to apply it.
If you select a photo which has keywords applied but those keywords are not in your Bridge Keywords list, then they should appear at the bottom of the list in italics under the heading "Other Keywords". If you wish to add those keywords to your Bridge list, right click and choose "Make Permanent". Then you may drag the keyword to a more suitable location in your list.
Hope this helps (and makes sense!)