32GB is the total installed storage in decimal units (a binary GB is 7% larger, so in binary this is 29.7GB).
However, this total includes space used by the system software and system cache. The storage is partitioned, and the space allocated for the system has to be large enough to allow for future updates. Hence what is available to you is what is left, which is always less than it says on the box - in your case about 23.5GB (binary) for the "storage card" partition ("/sdcard").
This is true for all phones, though Samsung tend to use more space for the system than most.
It's also true of any computer: the OS will have taken up a chunk of space. However, hard drives are so big that it's much less noticeable there.
There's a sticky thread about storage at the top of this forum if you want to see a bit more detail of how your phone uses the space.
http://imgur.com/pR1fRDi