Still no details of what shield you are using. (my first post / I do not have more info than that:
*** As a first project we try to get a motor run with the Arduino Uno rev. 3 ATmega328 and motorshield L298 ***.)
The code looks wrong for most of those I know. .....okay
1st the motors we have are crap.
2nd we have written a code ... in a loop (see here under) ....
the problem is that when starting the loop for the 2nd time the first block is ignored 
const int MotorRpinA= 12;
const int MotorSpeedpinA= 3;
const int MotorBrakepinA=9;
const int MotorLpinB= 13;
const int MotorSpeedpinB= 11;
const int MotorBrakepinB=8;
const int CCW = HIGH;//achteren
const int CW = LOW;//voorwarts
void setup() {
// motor A en B volle toeren
pinMode(MotorRpinA, OUTPUT);
pinMode(MotorSpeedpinA, OUTPUT);
pinMode(MotorBrakepinA, OUTPUT);
pinMode(MotorLpinB, OUTPUT);
pinMode(MotorSpeedpinB, OUTPUT);
pinMode(MotorBrakepinB, OUTPUT);
Serial.begin(9600);// serial monitoring
}
void loop() {
//start motoren L en R met max speed
//block 1
digitalWrite(MotorRpinA, LOW);
Serial.println("richting vw");
analogWrite(MotorSpeedpinA, 255);// max. snelheid
Serial.println("max snelheid R");
digitalWrite(MotorLpinB, LOW);
Serial.println("richting vw");
analogWrite(MotorSpeedpinB, 255);// max. snelheid
Serial.println("max snelheid L");
delay(5000);
digitalWrite(MotorBrakepinA, VW);
analogWrite(MotorSpeedpinA, 0);
Serial.println("Remmen R");
digitalWrite(MotorBrakepinB, VW);
analogWrite(MotorSpeedpinB, 0);
Serial.println("Remmen L");
delay(2000);
//block 2
//start motoren L en R met max speed achteruit
digitalWrite(MotorRpinA, HIGH);
Serial.println("richting aw");
analogWrite(MotorSpeedpinA, 255);// max. snelheid
Serial.println("Snelheid 200");
digitalWrite(MotorLpinB, HIGH);
Serial.println("richting aw");
analogWrite(MotorSpeedpinB, 255);// max. snelheid
Serial.println("Snelheid max aw");
delay(5000);
digitalWrite(MotorBrakepinA, AW);
analogWrite(MotorSpeedpinA, 0);
Serial.println("Remmen");
digitalWrite(MotorBrakepinB, AW);
analogWrite(MotorSpeedpinB, 0);
Serial.println("Remmen");
delay(2000);
return;
}