How to create my own functions?

Question

I am not quite to the tutorial where it discusses functions, but I am working on a project right now that I really want to create a function for. I am trying out this code:

#include <iostream>
using namespace std;

int main() {
int mathQuestion(int q){
if (q == 1){
cout<<"1. What is 1+1?"<<endl;
cin>>a;
cout<<"Your answer: "<<a<<endl;
if (a==2){
cout<<"Correct!"<<endl;
k+=1;
}
else{
cout<<"Incorrect"<<endl;
}
}
}

mathQuestion(1);
return 0;
}

My compiler gives me two errors:
1. a function-definition is not allowed here before '{' token
"int mathQuestion (int q){"
2. expected '}' at end of input (very last line