Google announced what the M in Android M stands for, and it's Marshmallow.
The Main features of android 6.0 are:
1. Android Pay:
Android Pay will let you walk into stores and tap on an NFC terminal to pay for products.
2. App permissions
Easy way to know which permissions are given to each apps
3.Standardised fingerprint support
A set of new APIs which will help the apps to be compatible with fingerprint support for enhanced security
A Feature which will improve your battery life
5.Simplified volume controls:
Know which app in making sound !