I don't know why I get this errors.

#include <SoftwareSerial.h>

#include <CapacitiveSensor.h>

/*
 * CapitiveSense Library Demo Sketch
 * Paul Badger 2008
 * Uses a high value resistor e.g. 10M between send pin and receive pin
 * Resistor effects sensitivity, experiment with values, 50K - 50M. Larger resistor values yield larger sensor values.
 * Receive pin is the sensor pin - try different amounts of foil/metal on this pin
 */
SoftwareSerial mySerial(2, 3);
byte byteData;
CapacitiveSensor   cs_8_5 = CapacitiveSensor(8,5);        // 10M resistor between pins 4 & 2, pin 2 is sensor pin, add a wire and or foil if desired
CapacitiveSensor   cs_8_6 = CapacitiveSensor(8,6);        // 10M resistor between pins 4 & 6, pin 6 is sensor pin, add a wire and or foil
CapacitiveSensor   cs_8_9 = CapacitiveSensor(8,9);        // 10M resistor between pins 4 & 8, pin 8 is sensor pin, add a wire and or foil
int note1 = 60; 
int note2 = 62; 
int note3 = 64;
byte note = 0; 
byte resetMIDI = 4;
void setup()                    
{
   cs_8_5.set_CS_AutocaL_Millis(0xFFFFFFFF);     // turn off autocalibrate on channel 1 - just as an example
   Serial.begin(9600);
   mySerial.begin(31250);
   pinMode(10,OUTPUT);
   pinMode(11,OUTPUT);
   pinMode(12,OUTPUT);
   
}

void loop()                    
{
    long start = millis();
    long total1 =  cs_8_5.capacitiveSensor(200);
    long total2 =  cs_8_6.capacitiveSensor(200);
    long total3 =  cs_8_9.capacitiveSensor(200);

    Serial.print(millis() - start);        // check on performance in milliseconds
    Serial.print("\t");                    // tab character for debug windown spacing

    Serial.print(total1);                  // print sensor output 1
    Serial.print("\t");
    Serial.print(total2);                  // print sensor output 2
    Serial.print("\t");
    Serial.println(total3);                // print sensor output 3

    delay(10);      // arbitrary delay to limit data to serial port 

if(total1>100){
  digitalWrite(10,HIGH);
  delay(1);
  noteOn(0, note1,100);
}
if(total2>100){
  digitalWrite(11,HIGH);
  delay(1);
  noteOn(0, note2,100);
}
if(total3>100){
  digitalWrite(12,HIGH);
  delay(1);
  noteOn(0, note3,0);  
}
else
delay(1);
digitalWrite(10,LOW);
digitalWrite(11,LOW);
digitalWrite(12,LOW);
noteOff(0, note1,0);  
noteOff(0, note22,0);  
noteOff(0, note33,0);  

delay(10);

}

ex1.ino: In function 'void loop()':
ex1:56: error: 'noteOn' was not declared in this scope
ex1:61: error: 'noteOn' was not declared in this scope
ex1:66: error: 'noteOn' was not declared in this scope
ex1:73: error: 'noteOff' was not declared in this scope

I don't know why??????

I don't know why??????

So, in what scope are noteOn and noteOff defined? None is the wrong answer.

You can't call a function you haven't written (or have no intention of writing).