(cr-gpg simply calls out to the gpg installation on your machine. Option  therefore is asking where it can find the gpg executable, and Option  is looking for a scratch directory to do its work). (We make some effort to ensure that the temp directory is well maintained). You should be able to click “Use Default” on most installations.
The “Encrypt to self” option is fairly self explanatory. If i encrypt (and send) an email to you, the encrypted email will be in my sent-items. I would be unable to read this mail though (since it has been encrypted with your public key, not mines). If you would like to be able to read the mails as well, then simply select this option (and enter your email address in the next field: “Encrypt to self Email Address”)
Now click “Save” to save these options. (cr-gpg will do some basic sanity checking on your options). You can return to these options through the extensions window or by clicking the lock icon added to your browser chrome
Convenience Functions :
The other convenience functions enabled through the lock icon allow you to do simple gpg key management, encrypt and sign blocks of text.
Embedded Functions :
When typing an email in GMail, we should now see an additional link: “Encrypt Message”
(If we have the recipients public key,) simply clicking this should encrypt the mail to the recipient as seen below.
When you receive an encrypted email, simply click on “Decrypt Message”.
Decrypting an email requires access to your private key (which is usually password protected.) Enter the password, Click “OK” and you should be good to go..