There are two types of keyboard shortcuts in Gmail.
1) Shortcut keys that are always active : Some of the shortcuts are always active whether you want or not.
2) Shortcut keys that you have to turn on : You have to turn on those keys to use. You can turn it on by bellow steps
Steps to turn on Shortcut keys in Gmail :
1) Click on the gear icon (At the top right corner)
2) Select setting from it.
3) In general tab (Default opened) scroll down a bit. There is an option to set keyboard Shortcuts On.
4) Save Changes and now you are able to use Shortcut keys.
I am listing here most commonly used Shortcut keys. Shortcut keys are for Windows users. For Mac user replace Ctrl by ⌘.
Keys which are always on
Ctrl + Enter : To send a Mail after composing is completed
Ctrl + Shift + c : To add a Cc recipient
Ctrl + Shift + b : To add a Bcc recipient
Keys which need to be turned on
c : To compose new mail
d : To compose mail in new tab
n : To send a new message
` : To go to Inbox
e : Archive mail
! : Report mail as spam
r : To reply
Ctrl+s : Save in Draft
f : To forward mail
Above keys are frequently used in Gmail. If you want to use more keys here is the link of Shortcut keys for Gmail. Shortcut keys make our work a lot easier and faster. Hope you like this post. If having any question or suggestion write it in comment.