Do this: gpg --gen-key
A series of interview question, just answer them accordingly. No worry, just a very simple question, you should able to answer. After this, get ready to encrypt the file.
Sending out this command: gpg --encrypt --recipient
This will generate an output file, called secret_file.txt.gpg. To decrypt the encrypted file, send this command:
gpg --output secret_file.txt --decrypt secret_file.txt.gpg