Click one photo, then hold Command and click other photos to select non-adjacent items
Click one photo, then hold Shift and click another photo to select a range of adjacent items
Drag to draw a selection box around multiple photos
In Finder, use Command+A to select all photos in the current folder
In the Photos app, hold Command while clicking individual photos to select multiple items
In the Photos app, hold Shift to select a continuous range of photos
On a trackpad, use click-and-drag to lasso multiple photos when available