How do I select multiple photos in the library?

Click Multi-select on the photo library toolbar. A check-mark appears beside the tool when it is enabled. With the Multi-select tool enabled, you can select multiple photos in an album by clicking the photos, without pressing any buttons on the keyboard.

Note: You can also use the standard Windows selection methods. To select photos in a row, click the first photo, hold the Shift key and click the last photo. This selects all photos in between. To select non-adjacent photos, hold the Ctrl key while you select photos.