Here's a little guide on terminology.
Script: A collection of letters that evolved together and go together for writing one or more languages. A script's letters constitute the more specific Alphabets. A, B, C, D, etc. are Latin Script. Likewise, א ב ג ד etc. are Assyrian/Hebrew Script.
Alphabet or Abjad: A collection of letters selected from the base script or derived from the script for a specific language. English uses the basic 26 letters of the Latin Script. Spanish uses those 26 letters too, but also uses the derived letters: á, é, í, ó, ú, ü, and ñ.
These terms are highly interchangeable, for instance, the Latin Script being called the Latin Alphabet. Many scripts are limited to a single language and are effectively both the script and the alphabet. However, scripts such as Arabic are used for many languages's alphabets, such as Farsi's, Urdu's, or Arabic's.
This isn't really linguistics, but that's okay.
Codes as what I believe you made, simply switch the letters of the alphabet around. For example, I want to send a message to my friend that says, "Hi." I put it through your encoder and get Xē. No one but him--since he has the cypher-- can understand it. He puts it through and gets, "Hi."
A con-script is made entirely of new symbols for any language, artificial or natural. You can see some in this forum's threads.
If you want to make one based on sounds (you write words how they sound), I suggest that you read the Wikipedia articles on the
IPA and
the IPA for English. Although you can always make a script with a 1:1 correspondence to the Latin alphabet.