I see you are new, so welcome to the forums.
Here is a link to
Audacity, which is a free open source program that can handle the formats required by FPSC.
I use the 1.2.6 version because it is more stable than the 1.3.4 Beta.
It's Audacious!
Once you have created your sound files then it is easy to get them playing in FPSC (via FPI scripts) with the sound or loopsound actions.
Creating a text message to display is called a "Heads Up Display" or HUD for short. They too are easy to achieve.
Be sure to read the PDF manual that came with FPSC in the Docs folder.
Also take note of the "Thread Subject Search" box at the bottom of this page.
Most of the time, you can find your answers there, and it helps keep people from posting the same questions.
Once again, welcome to the forums.
Good Luck!