XnView Software

Hi, I'm new to XnView MP and I am struggling to understand why there is a catalog?
Does it cater for meta-data perhaps that is not saved/embedded into individuals files?
I recently added a category to a pic via 'edit IPTC' and it appeared in the thumbnail label straightaway.
I later added a category to a pic by simply added a tick to the tick box in the category pane. This did not appear in the thumbnail label for some reason. Maybe its added to the catalog instead of being embedded in the pic meta-data?
I'm confused. I'm wondering whether I should disable the catalog altogether in settings, but I'm not sure of the consequences
Any help greatly appreciated!

Short explanation
One can give a "Category" to a file.
Categories are stored in the catalog. (Xnview.db file)
Then you can use "Categories filter" pane to find files having some categories.

If you enable "Export categories to ..." (Tools>Settings>Metadata), checking a category for selected files will write iptc or xmp normalized keywords for file types that support metadata (like jpg)

Using embedded Iptc or xmp (or xmp sidecar) metadata is a standard way to keep keywords strongly linked with your photos.
So, "categories" is a friendly way to manage keywords and to search in photos.

"Edit iptc" window is used to manage other metadata (captions, copyright, places...)

I just pasted a translation of a french text here :
viewtopic.php?p=179720#p179720

Thanks for the response michel038.

I need to find time to properly read and absorb what you said and then I may need to respond with more q's