The second grade, commercial, should be adequate. PGP will then ask you to enter a pgp userid. Next, you will have to enter a pass phrase that will be used in conjunction with your secret key as an additional security measure in case your secret key falls into the wrong hands. Enter a sentence or phrase that is simple enough for you to remember, but not totally obvious that someone might guess it. The pass phrase is case-sensitive and you may use spaces and punctuation.
Key generation is accomplished through the use of large truly random numbers.
The computer uses a fast timer to time the spaces in between the keystrokes you will enter to derive these random numbers. So when prompted, just type some gibberish at an irregular pace until it tells you to stop. You may have multiple keys on both your secret and public keyrings. When using PGP commands that use your secret ring, if you don't specify an optional userid, pgp will use the first secret key on the ring as a default. If you don't have one, read the documentation on the mail packages and learn how to create this file.