HOW TO View your photos
Years
The main options for viewing your photos (including all the pics on this Mac that you’ve imported, plus your iCloud Photo Library) are in the Photos view, which offers four tabs, starting with Years.
Days
The Days tab has the neatest view, with photos closely spaced, cropped to varying sizes. The layouts make more sense when you switch between views by pinch– zooming with the Magic Mouse or Trackpad.
All Photos
In All Photos, you can see every picture, scrolling vertically through time. The icon at the top left switches between cropping each photo to a square, as here, or showing its actual shape.
Months
Click the Months tab for a different layout, with some pics shown larger. Each item represents a “moment” — photos around the same time and place. There’s no Moments view as such, though, as on iOS.
Single photo
When you zoom into or double–click a photo from Days view, it’s enlarged. You can then click Edit at the top right to bring up Photos’ image–editing tools. Other apps can extend these: click the three dots to see.
Helicopter view
Zooming in and out in the All Photos view increases or reduces the thumbnail size. You can also switch between the four Photos views by holding the Cmd key and pressing 1, 2, 3 or 4.
In Books > Preferences > General > Sync, checking “Sync collections, bookmarks and highlights across devices” means just that: it doesn’t sync your actual books. To make Books show your purchased and imported titles from other devices, go to System Prefs, click Apple ID (to access icloud settings), check icloud Drive, Options and Books. Phew!
On the side
The first time you sync a device, connect it with its USB cable. Once it appears, you can check “Show this [device] when on Wi–Fi” and it’ll appear in the sidebar whenever it’s on the same network, without a cable.
One at a time
If iCloud sync is active on this device, the Finder will only offer to sync content that’s on this Mac but not in iCloud. A “Remove & Sync” alert refers to content synced from other Macs; iCloud content is unaffected.
Inside job
The Files tab still doesn’t offer a general purpose file transfer facility, instead just syncing data associated with individual apps. iCloud Drive is now generally a superior way to make files available elsewhere.
find My MAc and Find My Friends are now one app, Find My, with tabs for People and Devices. Behind the scenes, finding devices gets a lot cleverer, as long as you own two Apple products. All Apple devices will constantly broadcast Bluetooth signals that only other Apple devices recognize, containing a public key unique to their owner. Any receiving device uses this to encrypt its location, sending the data to Apple. When you look for your first device using Find My on your second device, it uploads a matching public key to Apple, which searches its records and returns any relevant data. Your second device has the private key to decrypt the location and tell you where the first device is. So your device could be found, via nearby Apple users, even if offline, unknown to anyone but you.