Drag & drop images
When accessing the Add images section, you will be able to drag & drop images from your computer.
Due to browser limitations, you will not be able to add more than a few dozen images at the same time. The limit also depends on the average size of your images.
You should not leave or reload the page.
That step corresponds to the effective upload of the images from your local computer to the remote servers.
After adding images via drag & drop, you can find those images in the Explore images tab. In that tab, without any other sorting, the images are sorted by batch. You will then find the images you've just uploaded on the last page of the section. However, within a given batch, the order of the images will not be exactly the same as the order in which you dragged the files.