how to declare functions in c++

Iam writting a code to add two numbers but i want to know were to declare the add function in the code, how can i do with so ?

it's for an android phone version

include

include(cmath);

using namespace std;

int main() { int add(num,num)

cout<<"enter two numbers";

cin>>"number1, number2";

sum = int add(a,b);

cout<<"sum"<<;

return 0;

}

I EXPECT THAT THE OUT PUT OF 2+5 TO BE 8 BUT ITS TELLING ME ERRORS ONLY