When you upload photos to a page, all the photos can be found here in the All Photos section. You can also upload photos here first then select them to add them to a page.
Below each thumbnail there is a checkbox icon. Check that checkbox to select the photo. When you do, you will see a tray open at the bottom of the screen. That tray has options for creating a new page then add the photos to that page, deleting, add tags, etc...
To select multiple photos in a row, click the first checkbox, hold down your shift key on your keyboard, then select the last photo you want to select.
Adding tags to photos helps you find photos.
Recent Upload Sessions
Whenever you upload photos either from this section or to a page, it creates an upload session. By clicking the upload session, you will see all photos uploaded at that time. You have the option to select all when viewing an upload session.
Photo Titles, captions and tags
When clicking on a thumbnail you will be able to view the photo larger and add a title, caption and tags. If you already have a title & caption in the photo IPTC data, it sytist will try to import those when the photo is uploaded.
Default sort of the All Photos section
You can change the default sorting view in the Settings -> Photo Sizes & Defaults section.