Some space is reserved for your OS. Having 11.88GB is normal.
If not enough, get microSd card and don't expect to get full 32GB,
you'll get arpimd 29GB++ from a 32GB microSD card.

i9300 is the model, which is actually GT-i9300.
The general name is Samsung Galaxy S3.
Other countries may be using other model number such as SGH-i747.

there's only 16GB model available in malaysia.
you can get 32GB model from other countries.
The capacity refers to the internal storage.

You can add on external storage in terms of MicroSD in up to 64GB.

malaysia currently is 16gb
urs showin 11.88 is 16gb