Java beginner question please help

Question

class MyClass {

static void sayHello() {
System.out.println("Hello World!");
}

public static void main(String[ ] args) {
sayHello();
}
}
// Outputs "Hello World!"

1)why do we need static void in the sayHello() method?what does it mean when we include them?

2)if we add in public to sayHello() method,does it make a different to this code?does it mean i can use this method in other classes if i add the word "public"