I’m building a Rc car and I have the arduino Uno. I had quetion if I could power the dc motor up to 15V (connected adfruit Motor shield), what dose it mean that the Arduino can only operate with 5v?
The Arduino’s chip can only handle up to 5.5V. You can put more voltage into the DC barrel jack on the board. I believe the highest voltage input would be 12V before you would need to put a heatsink on the voltage regulator.
So if you want to put the 15V into the Arduino, you can, but you will need a heatsink. Or you could search ebay for a “buck converter.” You could put one of those before the Arduino to regulate the voltage down below 12V. I would advise somewhere in the range of ~9V to keep things safe.