The fastest way to add images into your Media Library is by bulk.
To do this, go to Media in the left-hand menu, and select Add New from the flyout.
Click the Select Files button and browse to the folder containing your prepared images.
Here you can change to icon mode in your file browser so you can see the files, but if you know that all the files are ready to go, just select them all (Cmd+A).
You can select or deselect items by clicking on the individual images while holding down the Cmd key.
When the images are uploaded, the title field is automatically written with their filename.
Check the titles, captions and Alt text. (Alt text is information about the image in case it doesn’t appear for some reason. It is also the text used by auto-readers for sight-impaired users.)
Then tag each image according to it’s Media and Portfolio categories. See ‘Media’ in the Editor Interface article.
You can also automatically populate the caption field for each image. Refer to Using XNview.