Google publishes exhaustive Android 6.0 Marshmallow quick start guide
Google's official quick start guide for Android 6.0 Marshmallow can be downloaded for free from Google's Play Store. You can read the guide on your Android smartphone or tablet, but you can also view it on your computer for what's arguably a better experience.
62 pages long, the quick start guide takes you through the features that are new in Android 6.0 Marshmallow (such as Google Now on Tap, heterogeneous storage, Doze, and App Standby), but then moves on to demonstrate tricks that have been available since previous Android flavors such as turning on the flashlight, customizing the homescreens, using Android Wear and Android Auto, or setting up multiple user accounts.
If you're new to Android, then Google's official guide to Android 6.0 Marshmallow is the perfect resource to get you on your feet!