Recent and updated articles

Which displays support True Tone, as available in MacBook Pro 2018 models
How to reset the System Management Controller (SMC) on your Mac updated for the latest models
If your Mac’s fans run at full speed when started up (with important note for MacBook Pro 2018 models)
Selecting a different startup disk using the Startup pane and Startup Manager
How to install Windows using Boot Camp
Adding equations and maths in Pages, Number, Keynote (macOS and iOS)
LaTeX and MathML support in Pages, Numbers, Keynote, iBooks Author
How to use advanced options in Pages to fine tune or create a digital book in the EPUB book format
Connect your Apple ID to your Movies Anywhere account and watch eligible movies across all of your devices. (US only.)
iPad USB power adapter certifications
How to restart a Mac using Screen Sharing or Remote Login (SSH), even when FileVault is enabled on the remote Mac (Sierra and earlier). Uses fdesetup. Recently archived, but valuable for those using FileVault 2 in Sierra and earlier.
Using tethered caching to update content on iOS devices. For Sierra; High Sierra features its own caching service which replaces this.

New MacBook Pro and T2 chips

About SSD encryption in new MacBook Pro 2018 and iMac Pro models with the T2 chip
About Secure Boot in Macs with the T2 chip
About Macs with the T2 chip
Identifying different models of MacBook Pro
Startup Security Utility for Macs with the T2 chip
Macs with the T2 chip don’t support starting up from network volumes
What to do before you sell or give away your Mac updated for MacBook Pro models with a Touch Bar

iCloud

iCloud.com is the web interface to iCloud, accessed through your browser. This offers several valuable tools which are not available in macOS or iOS, which Apple details in a series of useful articles.

Using iCloud Drive on iCloud.com
Using iCloud.com to view and edit Pages, Numbers, or Keynote files
Create an email alias in iCloud Mail
Automatically forward emails in iCloud
Report junk invitations in iCloud Calendar

Other useful iCloud articles include
If your iCloud documents and data aren’t the same everywhere
Manage your iCloud storage
Help with iCloud Photo Library
iCloud Photo Sharing
Help with iCloud Keychain

Reference

Supported printers and scanners in macOS High Sierra, Sierra, El Capitan, Yosemite, and Mavericks
TCP and UDP ports used by Apple software products
Fonts included with macOS High Sierra
Digital camera RAW formats supported by iOS 11 and macOS High Sierra
List of available trusted root certificates in macOS High Sierra
Final Cut Pro X: Final Cut Pro: Supported media formats
How to download macOS Sierra
How to download apps and content again from Apple’s stores

Reporting phishing and other attacks to Apple

macOS Deployment Reference

iCloud and other online service status
Wireless carrier support and features for iPhone in world regions

Security updates

Links to the release notes detailing the security content of each macOS update in 2018.

Apple security updates main page
High Sierra 10.13.5, Security Update 2018-003 Sierra, El Capitan
Security Update 2018-001 for High Sierra
High Sierra 10.13.4, Security Update 2018-002 Sierra, El Capitan
High Sierra 10.13.3 Supplemental Update
High Sierra 10.13.3, Security Update 2018-001 Sierra, El Capitan
High Sierra 10.13.2 Supplemental Update

Last updated: 16 July 2018.