personally i just used the serial output sketch to test my
wiring. keeping unknowns to a minimum..
if you take a look at the sketch included with the library by kg4wsv
its functions much like any lcd. you can write to it from
anywhere in the program with commands like
osd.write_to_screen("hello world. This is a test", 3,9);
(3,9 start being location)
or values with osd.print(SomeValue, DEC);
i havent played much with it myself. i just used it for a rather simple
timestamp overlay box. that now works and is put away 
i posted my RTC example sketch in my previous post.
might upgrade to using a GPS input for time. as im having issues
with my real time clock accuracy..
(currently have 6 of them running on a breadboard to pick the best crystal.. and this is at room temperature. Sigh!. )
anyway
Hope that clears it up a bit!.
think of it as a serial attached LCD..
/Kyndal