Takto to je

char inString[32];
int inCount;

void setup() {
       Serial.begin(9600);
       pinMode(13, OUTPUT);
       //digitalWrite(13, HIGH);
}
void loop()
 {
   inCount = 0;
 
 while (Serial.available() > 0)
 { 
   inString[inCount] = Serial.read();
   delay(10);  
   if (inString[inCount] == '\0') break;
   inCount++;
 }
 
 inString[inCount] = '\0'; 
  
 if (inCount > 0) { 
    Serial.println(inString); 
    if(inString == "kokot")digitalWrite(13, HIGH); 
}
}