How do I use shortcut keys in Gmail?

Question

I want to start using shortcut keys in Gmail. Where are they documented? Can I just start using them, or do I need to activate a feature for them somehow?

There are lots of questions in this Webapps SO site about specific Gmail shortcuts, but this more general question doesn't seem to have been asked!

Answer 1

A quicker way to view (and enable shortcuts if they are disabled) is to simply press

SHIFT + ?

This will display a popup with all the keyboards and also a toggle to enable or disable them.

Answer 2

As to the answer given, the following update:

As per 11 April, Gmail will have activated a few shortcuts that can't be de-actived.
See following two references:

1. Google - Keyboard shortcuts
2. googlesystem.blogspot

Answer 3

Yes, you have to activate a feature and yes, they are documented. See below.

To activate the shortcuts:

1. Click on the gear icon from your upper-right corner
   
2. Click on Mail settings
3. In the General tab, search for Keyboard shortcuts - the second group from the top
4. Click on Keyboard shortcuts on
5. Scroll at the bottom of the page
6. Click Save Changes

The list of keyboard shortcuts and their description/function can be found here.