I am going to post my reply without reading the other replies. Simply put, you can "kick the tires and light the fires" and go flying. But that comes with a lot of assumptions - check for proper fuel level depending on mission, check oil, proper preflight, ect. Now if you are planning a trip from point A to point B, you may have to take into account loading calculations, fuel load and burn, wind speed and direction, ect.
It really all depends on the type of aircraft you are intending to fly and what your mission is. The more complex of either and the more flight planning you will have to do, typically. That is a very watered down and simplified answer. Now I will read the other posts...
