Why are all these emu's so hard to find the exit button for? The answer is.... the dev's correctly knew that you wouldn't want an exit button.
Afterall, you spent good money upfront and time in droves in a pre-order queue to obtain 'the device with controls' that their awesomeness is presented on for free.
Prometheus (who cannot be emulated) is of course correct though, each PND usually includes documentation via XFCE or Minimenu (the key is patience though, as the default program to open the varied formats these docs are in, is very very slow to open). The download site, dev's page or original creators page the porter's (sounds somehow like a lowly hospital job yet is vital) have linked with their hard work in spare time, will also likely show the controls for the application in question.
Sometimes things have been ported in a rush though but now more people are about, with Pandoras in the wild to boot (meow), such questions will arise which will prompt the original dev's, (or new folk with the know how and desire to), to remap said controls, add in icons for the PND and ensure that it follows the PXML standards and appears where it should (like Mr Ben's shop-keeper, who is a valid shopping comparison to the Pandora experience and its gamut of possibilities yet to be explored) upon the menu.
I have rarely seen Prometheus suggest even an almost RTFM attitude to any question, as she is afterall Empress Wu of the How of Pandorian Knowledge. So once again, she has shown her keen eye, mastery of the subject and right of will alone the bequeathment of a level zero to all who fail to heed her kindly (Pandora typed) word, as neophyte or disciple. Tickles is under written warning of being watched and at all other times, do as the Prometheus in word and deed and be helpful, cheerful, knowledgeable and specific on your trivia. Leave the flame bait for the trolls of this level and proceed with stealth upon the bridges you have to cross to proceed as you have to cross and may need to turn back, so dont burn em as you pass.