when I connect the arduino one to 12v and connect a servo to the arduino the arduino overheats and restarts itself
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richardeja:
when I connect the arduino one to 12v and connect a servo to the arduino the arduino overheats and restarts itself
Don't worry! Did the same thing myself. For Motors, use a motor driver with separate power supply. This prevents a lot of power loss from the UNO. This can damage the board as well I've heard. Make sure to keep the board in it's voltage limits. 
Happy Easter!
-Englishscone
With 12v on barrel jack or Vin pin, you can draw very little current before the regulator begins to overheat - it is a linear regulator, dropping the excess voltage as heat. With 12v, that means most of the power coming in is being dumped as heat (7/12th's). It's best to use a 7~9v supply when using the on-board regulator.