I was wondering the same and then read the big red text KNOWN ISSUE: If you happen to find the difficulty settings panel, it does not work and was not meant to appear yet because it isnt finished. Sorry!
This should answer your questions about interplanetary travel http://forum.kerbalspaceprogram.com/threads/27236-Tutorial-Step-by-step-Interplanetary-Hohmann-transfer-guide-and-tips