Last time I created a PSP page was about 2 years ago. I created a HTML file with embedded PL/SQL and the used the PSP converter/uploaded to load it into the database. The upload then creates a PL/SQL procedure/package (not quite sure) in the database which can be executed via the PL/SQL mod on the IAS server. PSP was in a way their version of JSP (Java Server Pages HTML pages with Java embedded into them which when executed were converted)
I personally used designer to design generate Web PL/SQL forms as I found it more benificial at the time.
Maybe PSP has moved on since then have a look at this thread and see what other people think.
1. Install the PL/SQL Toolkit
2. Create the Listener
3. Create a Database Access Descriptor
4. Create an Application called pspApp
5. Add a Cartridge to your Application
6. Create the PL/SQL Server Pages Script
7. Load the PL/SQL Server Page
8. Verify Procedure creation
9. Reload OAS
10. Execute the PSP script from OAS