In C/C++, the term is function, not procedure, though they mean similar things. One thing that newbie and robtillaart left out (not intentionally, I'm sure), but that you must not, is the return type for the function.
All functions must have a return type defined. If the function returns nothing, its return type is void, but that must still be explicitly called out.
[glow]void[/glow] procedure1()
{
if (X==Y) // Note the double == is a compare, the single = is a assignment
{
Serial.println("X equals Y "); // or ...
}
}