i dont know if this code it ok

 int mul;
 int num1;
 int num2;

void setup() {
 Serial.begin(9600);
 
}

void loop() {
Serial.println("enter number 1");
while(Serial.available()==0)
{
}
num1=Serial.parseInt();
Serial.println("enter number 2");
while(Serial.available()==0);
num2=Serial.parseInt();
mul = num1*num2;
if(mul>100)
{
  Serial.print(mul); 
}
}

What happened when you tried it?

The Arduino system is great for learning-by-doing.

…R
Serial Input Basics - simple reliable ways to receive data.