Happy new year!

You can start here https://www.arduino.cc

This sketch flashed in your new Arduino

// consts
int const maxBrightness = 225;
int const baseFade = 1;
int const leftPins[] = {9, 10, 11};
int const rightPins[] = {3, 5, 6};

// vars
int brightness[3];
int fade[3];
 
void setup() 
{ 
 // set pins to out mode
 for(int i = 0; i < 3; i++)
 {
   pinMode(leftPins[i], OUTPUT); 
   pinMode(rightPins[i], OUTPUT);
 } 
 // set init vals
 brightness[0] = 0;
 brightness[1] = maxBrightness/2;
 brightness[2] = maxBrightness;
 fade[0] = baseFade;
 fade[1] = -baseFade;
 fade[2] = -baseFade;
}
 
void loop() 
{
 for(int i = 0; i < 3; i++)
 {
  // set brightness
  analogWrite(leftPins[i], brightness[i]);
  analogWrite(rightPins[i], brightness[i]);
  // calculate new brightness value
  brightness[i] += fade[i];
  // reverse fade on border vals
  if (brightness[i] == 0 || brightness[i] == maxBrightness) 
  {
   fade[i] = -fade[i] ;
  } 
 } 
 // wait
 delay(5);              
}