There are three distinct passwords used in the MyProxy uploading process.
This is set when you export the .pfx file from your browser. If you want to access the certificate and private key stored in the .pfx file, you need this password. When you create .pem files from the .pfx, the private key file userkey.pem receives this password by default. The certificate usercert.pem is public and doesn't require a password.
This password protects the private key corresponding your personal certificate. The file userkey.pem is protected by this password, and by default when created it is the same as the password of the .pfx file from which the key was extracted. You may also see this password called the 'certificate password' or the 'grid password'.
This is a password specified each time you upload a proxy to a MyProxy server. To retrieve the proxy you will need the MyProxy name and MyProxy password. Each proxy uploaded will need a new name and a new password.