Directly from notifications you can read the essence of the message, Mark as read, or Reply (by default). By Pinching-out on the notification in the “Notifications Center”, you will be prompted with the following options: Reply, Mark as Done and Delete.
You can customize these actions in the Notifications Center by tapping More (o o o) | Global | Customize Menus | Configure Action Buttons | Configure Notification Actions
For Nougat users, first ensure that the Nougat Notification option is enabled <blix>option is enabled</blix>, then you can customize these actions in the Notifications Center by tapping More (o o o) | Global Settings | Customize Menus | Configure Action Buttons | Configure Wear/Nougat Notification Actions.