void functions() not executing

long dur, dist;
const int trigPin= 10;
const int echoPin = 11;
const int SpdL = 9;
const int SpdR = 6;
const int ForwL = 7;
const int BackwL = 8;
const int ForwR = 4;
const int BackwR = 5;
int test = 1;

void setup() {
  Serial.begin(9600); //starts communication between arduino and US sensor
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  //last two lines define pins 13 and 12, respectively, as output
  
  pinMode(ForwL, OUTPUT);
  pinMode(BackwL, OUTPUT);
  pinMode(SpdL, OUTPUT);
  pinMode(SpdR, OUTPUT);
  pinMode(BackwR, OUTPUT);
  pinMode(ForwR, OUTPUT);
  //sets connected pins on arduino to output signals
}

void loop() {
 
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  dur = pulseIn(echoPin, HIGH);
  dist = (dur * .0343) / 2; 
  Serial.print(dist);
  Serial.println("cm");
  

  void forward();
}
void forward(){
  analogWrite(SpdR, 210);
  analogWrite(SpdL, 200);
  digitalWrite(BackwL, LOW);
  digitalWrite(ForwL, HIGH);
  digitalWrite(ForwR, HIGH);
  digitalWrite(BackwR, LOW);
  //go forwards
}
void backward(){
    analogWrite(SpdR, 210);
    analogWrite(SpdL, 200);
    digitalWrite(BackwL, HIGH);
    digitalWrite(ForwL, LOW);
    digitalWrite(ForwR, LOW);
    digitalWrite(BackwR, HIGH);
    //go backwards
}  
void left(){
    analogWrite(SpdR, 210);
    analogWrite(SpdL, 160);
    digitalWrite(BackwL, HIGH);
    digitalWrite(ForwL, LOW);
    digitalWrite(ForwR, HIGH);
    digitalWrite(BackwR, LOW);
    //turns robot left 
}
void right(){
    analogWrite(SpdR, 210);
    analogWrite(SpdL, 160);
    digitalWrite(BackwL, LOW);
    digitalWrite(ForwL, HIGH);
    digitalWrite(ForwR, LOW);
    digitalWrite(BackwR, HIGH);
    //turns robot right 
}
void stop(){
    digitalWrite(BackwL, LOW);
    digitalWrite(ForwL, LOW);
    digitalWrite(ForwR, LOW);
    digitalWrite(BackwR, LOW); 
}

I put the different movements under void functions() and none of them are working. Am I writing them correctly?

In loop() you have void forward(); this is just a functional prototype.

Use:

forward();

The other 3 functions are not being ‘called’ in loop().

Okay, I did not know that, thank you!

the code you have posted contains just the definitions of your functions forward, backward, left, right positionied inside function loop.

Usually these definitions are positioned outside of function loop()

Then inside of function loop() you put calls of the functions

take a look at these examples
https://startingelectronics.org/software/arduino/learn-to-program-course/15-functions/

best regards Stefan