Photos

The Photos app lets you view, edit, manage, and share photos stored on your PC, phone, OneDrive, and, optionally, Apple iCloud.

Where did it go?
The Photos app is all-new in Windows 11: it replaces an app by the same name from Windows 10 that also included an integrated video editor. That video editor is no longer necessary because Windows 11 includes a separate but superior video editing solution called Clipchamp. But if you are familiar with the old Windows 10 Photos app and would still like to use it for some reason, you can do so: it's available in the Microsoft Store as Microsoft Photos Legacy.
Photos consists of two primary experiences:

Photo viewer Photos is configured as the default app for common image file formats like BMP, GIF, HEIC, JPG/JPEG, PNG, and others. So when you open such a file, the Photos app's photo viewer window will appear and display the image.

Photo browser. When you run Photos from the Start menu or elsewhere, you are presented with the full app experience, which includes a navigation pane called the filmstrip for accessing different photo sources and a gallery feed view with thumbnails of your photos across the currently selected source. The default view displays all of your photos across all configured sources together. But you can select any source in the filmstrip to only display photos from that source.

Use Photos to view one or more images
Because Windows 11 uses Photos as the default viewer for most popular images format, this app will launch in its photo viewer mode when you open a supported image file.
Photo viewer basics
Photos offers a relatively sophisticated photo viewing experience. If the image you are viewing is the only image in its folder, the Photos app will display the image with its toolbar and no other controls.

But if there are other images in that folder, Photos will display navigational controls that include "Previous" and "Next" buttons on the sides of the app window and a pane of thumbnails representing the other images.

You can also type LEFT ARROW or RIGHT ARROW to navigate between each image in the current folder.
The "Previous" and "Next" buttons auto-hide and will reappear if you mouse over to one of the window edges. And you can toggle the display of the filmstrip by clicking anywhere on the image you're viewing.
You can also toggle the filmstrip display by typing F.
The filmstrip also lets you select multiple images to perform a limited range of actions across two or more images. This is described in the next section.
You may be surprised to discover that typing ESC will close the Photos app when used in photo viewer mode.
By default, the Photo app's photo viewer experience will display images at their normal size, unless the image is bigger than the app window, in which case it will fit the image to the window. But you can also zoom in and out of an image using the scroll wheel on your mouse.
Or, type CTRL + PLUS to zoom in on an image or C...