Not sure exactly what you are after Sheila.
The names down the left side are "Tags". So if you have a tag called "Birds" and you have named/tagged your images correctly, clicking on "Birds" will bring up all the birds in your gallery.
However if you also tagged some of your birds, with a secondary tag i.e Robins, then clicking on "Robins" will just show Robins. As you can imagine you will soon have loads of tags listed down the lefthand pane
I've never used Windows Gallery, so I'm not 100% sure, but to delete tags I think you will have to do each image seperately.
As an example if you had mistakenly tagged a thrush as "bird, thrush and robin" What you need to do is left click on the image and in the right hand pane right click on the offending tag, in this case "robin" and select delete.
Over the years I also saved all my photos to dedicated folders and sub folders, so most of my photos are not tagged, something I'm now correcting, but I'm using Adobe Lightroom