Arduino uno won't "accept" my sketch

I've tried everything what the website reccommends, but it still does not work.
I do want to put a disclaimer: I am not the very best in programming (but I do want to learn!).

Example:

the problem:
avrdude: stk500_recv() : programmer is not responding
avrdude: stk500_getsync() attempt 1 out of 10: not in sync : resp=0x77

this goes on 10 times (1 out of 10, 2 out of 10 etc.)

my sketch:

void setup(){
pinMode(6,OUTPUT);
pinMode(5,OUTPUT);
pinMode(4,OUTPUT);
}

void loop(){

digitalWrite(6,HIGH);
digitalWrite(5,LOW);
digitalWrite(4,LOW);
delay(2000);

digitalWrite(6,LOW);
digitalWrite(5,HIGH);
digitalWrite(4,LOW);
delay(1500);

digitalWrite(6,LOW);
digitalWrite(5,HIGH);
digitalWrite(4,LOW);
delay(1500);

}

It has nothing to do with the code ( pointless to post it) but everything to do with your USB to Arduino connection.