Execute a function?

I'm completely baffled here. I've created a function, but how can I execute
it? I tried opening up the SQL editor window and typed:

test_function(20, 32);
received: ERROR:  syntax error at or near "test_function" at character 1

I then tried:
EXECUTE my_function(20, 32);
received: ERROR:  prepared statement "test_function" does not exist

What the heck do I have to do to execute my functions to see the results of
them? The function exists, it shows up in the list of functions for the DB.
This seems so stupidly simple, and it probably is, so what am I doing wrong?

Thanks,
Steve