RTF - Ready to fly, includes all you needed to fly, with receiver already plugged in, motor (or EDF), ESC servos, retract(in any) already installed, and it comes with a radio transmitter, battery and charger. You will still need to charge the battery, put batteries in the transmitter (transmitter battery not included), install wings and stabilizers, etc.
KIT - It doesn't comes with any electronics , radio, receiver, motor, ESC, servo. KIT planes from different factories have different level of completeness. FMS , Dynam and Freewing, etc KIT planes are all painted, partially assembled, with all the plastic parts already installed on the fuselage, normally retracts are also already installed (if any), level of completeness are very high, factories tries to complete everything they could for a KIT plane ( without the above mentioned parts) while the planes are still be able to put in a shipping box. KIT planes from some factories are not assembled at all, like X-UAV, X-UAV KIT planes will come with all parts and foams unassembled, but their planes are simple designed, so its not that difficult to glue and assemble the parts together.
KIT+ - KIT Plus, it simply a KIT plane plus the mentioned parts, for example, KIT+motor+propeller, the KIT plane will come with motor (or EDF) and the required propeller seperately. The mentioned parts will be put in the same shipping box as the plane, but they may not come installed.
Notes for Beginner:
Before your first flight. Here is a list of suggestion:
1. Practice in simulator, nowadays many high quality apps are available, you can practice with your phone! Make sure you won't confuse with the direction, make sure you can control the plane in the way you think, and most importantly, make sure you can land the plane safely. Search Pica Sim, Leo's Sim, Real Flight with your phone.
2. Learn how to set the plane properly, for example, ESC initialization, and make sure the aileron, rudder, elevator movement matches the transmitter stick movement, reverse the direction if needed. If motor spinning direction is wrong, you can reverse it by swapping any 2 out of 3 wires connecting to the motor from ESC, or set ESC to reserve the direction( if ESC has this functions).
3. Make sure the CG (Center of gravity) is correct, location of CG is provided by factories and you can find this information from Manual. If the CG is wrong, 99% sure you will crash. Read more information from the internet, don't fly before you got enough knowledge and practice.
4. Make sure landing gear is glued tightly, screws are not over tightened (it would break the plastic parts)
5. No parts are loose. Battery wouldn't move inside the plane.
6. Set zero before you install the servo horn, that means make sure the servo is in the center position before you install the servo horns and glue the servos to the plane.
7. Unplug battery before turning off the radio. (very important!) Or else you may get serious injury. (Until you know how to set fail safe which make sure when no radio signal, throttle is set to certain level or zero)
8. Check the plane before every take off. After each landing, check motor and ESC temperature, if anything is hot, don't fly, or it will melt down plastic parts, or it would just stop spinning anytime. If so, check propeller balancing and check if the motor not spinning smooth, both situation could increase the current significantly and cause something burning hot. High current loading will cause ESC blow as well.
9. Learn how to protect your Lipo battery, don't let the Lipo battery discharge to lower then 3.7 v for each cell. you may put a low battery alarm in the plane or count the time if you know how long the flight should be.
10. Get help from experienced pilot. Do not make your first flight before have a check by experienced pilot.
11. Playing RC planes always accompanied by fixing planes, your planes would live longer when you got more experience.
There is no product in the market that guarantee you will have successful flight, the planes cannot stop in the air. When you feel something wrong when the plane is flying, it is too late and it could crash in the next 0.5 second. In average, the first flight last only as short as 30 seconds. So be prepared very well before your first flight.