What you need to know is that you can sign using your private key, but you can't encrypt without the recipient's public key;
you cannot verify signature without knowing the sender's public key, but you can decrypt it with your private key if the sender encrypted it using your public key.
Follow instructions here, but if you want a quicker way:
- Download and install gnupg-w32cli-1.4.9.exe from ftp://ftp.gnupg.org/gcrypt/binary/gnupg-w32cli-1.4.9.exe
- Install Thunderbird 3.x, and open Tools -> Add-ons -> Get Addons -> choose Enigmail to "Add to Thunderbird". (Would you will be asked to restart Thunderbird, do so.)
- Click Key Management
- Click Generate key
- Choose email
- Enter new password twice and rember it well, write down somewhere on paper safely.
- Generate revocation key.
- Select your e-mail in the Key Manager, and File->Explort your keys to a file.
- When saving your private key, and revocation key, save them to an encrypted volume.