You need first to relate your FTYPE_Code to a field (in your shape file) with long integer. (read esri help)
A couple of methods are to use a "distinct" or run dissolve on the ftype_code field and you will end up with a table of codes and values (your former ftype_code field).
Create your new feature class and associate the subtype (key in all subtype values)
Then I would use the esri simple loader found on the right click of your feature class.
- create a new field for your subtype code of type long integer.
- create your feature class (use your shape file to import the schema).
- use the properties of your gdb to create the subtype.(right click)
Use this tutorial to complete this step.
use the simple data loader... (right click your feature class to start)
Now that your gdb schema is ready you can load your shape file.
Now choose to load your features into a subtype.
(Note: you will need to load each subtype one at a time).
You will do that with the query builder in the last stage of simple loader.
When you understand all this you can probably script all this in modelbuilder.