which is the private gpg key?

Hi I'm still trying to sign up the code of conduct. I know I am boring and you might think that if I am so ignorant I should consider resigning instead of signing. But still I am in love with this project, and am not a person who gives up easily. I gave my fingerprint to ubuntu server and received to my gmail account the encrypted e-mail to answer. I followed all the instructions and downloaded the firefox modification that allow to decrypt the contents of the e-mails. Anyway when i ask to decrypt the conten of the e-mail the program asks me my private key. I tried many, but none seem to work. To generate my keys I used seahorse. Can anybody tell me which one is the private key i have to insert in that blody dialog box?
Thanks from despair.
Sun_tzu