Salts are extra bits of text which are used to make encryption tougher to break.  In sqlencryption.php a salt was used to encrypt and then to decrypt the data.  If you changed the salt from mysalt to something else and the encrypted data would change.  This prevents someone from simply decrypting your encrypted data.  You should therefore choose a complex and hard to guess salt.  With a simple salt a hacker could get your data by simply repeating the decryption with all possible salts until they get an intelligible string out (it would probably be cheaper to pay someone to kidnap you and get the salt from you!) .

Hashing and salts

Although hash() does not expect a salt in the same way as AES_ENCRYPT you can add a salt by manually joining it to the string of text before encryption.  Use phpencryption.php to encrypt a simple word and try to remember the first few digits of the encrypted version.  Then change this line:

$encryptedFirstname=hash("sha256", $firstvalue);

to this:

$encryptedFirstname=hash("sha256", 'anything'.$firstvalue);

That concatenates some text on the front of the actual data before encryption which is, in effect, a salt.  Try the page and the same string should be encrypted differently.

As before you should actually try to use as complex and random a salt as possible.  You could even add a second salt on the end as well.  As this is one way encryption you do not need to worry about how to remove the salt on decryption you just need to compare the two encrypted values when someone logs in with their password.