Introduction
There are two types of encryption methods: symmetric and asymmetric.

1) Symmetric Password Based Encryption - This is the simplest form of encryption.  It is a symmetrical encryption method. The same password is used to encrypt and decrypt the data (or the file).  This method is useful to encrypt sensitive information for yourself, or for family, or for a few trusted friends or coworkers.  

2) Symmetric Secret Key Based Encryption
This is the simplest form of key based encryption. It is a symmetrical encryption method. The same secret key file is used to encrypt and decrypt the data (or the file).  This is not a very commonly used technique.

3) Assymetric public/private Key Based Encryption
A public key file is used to encrypt the data. The corresponding private key file is used to decrypt the data. Only you should have access to your private key. You can distribute your public key to anyone who needs to send you data.  This is the technique that is most commonly used in corporations.

OpenPGP encryption
This is the most popular encryption method.  Many corporations employ OpenPGP encryption to exchange or store sensitive data. 
 

OpenPGP keys
To get started you would need to create an OpenPGP Key pair.  The private key should be stored carefully.  The public key should be distributed to your friends, collegues, customers or clients etc..

Encrypting and Decrypting files
Your customers or clients can use your public key to encrypt a file..  Then email the encrypted file to you.  The encrypted file can only be decrypted by your private key.  If the email is intercepted, no one will be able to decrypt the file since they do not have your private key.  Similarly if you need to send a file to a client, you should use the clients public key to encrypt the file.  Only your client has his private key to decrypt the file.

Signing and Verifying files
To confirm that you have sent the file, you should use your private key to sign the file.  Your clients can then use your public key to verify that the file was sent by you.

Encrypt & Sign
OpenPGP software normally support one step encrypt and sign.  This allows you to encrypt a file using the recipients public key.  At the same time, this also signs the file with your private key.  When the recipient receives this file, he can use his private key to decrypt the file,  and use your public key to verify that it was indeed sent by you.