It's probably easier to understand if you leave the redundant parens out because they serve no purpose:
var something = function() {
return 3;
} // <-- a function.
(); // now invoke it and the result is 3 (because the return value is 3) assigned to variable called something
console.log(something) //3 because the function returned 3
var something = function() {
return 3;
}; // a function is assigned to a variable called something
console.log(something) //logs the function body because it was assigned to a function
console.log(something()) //invoke the function assigned to something, resulting in 3 being logged to the console because that's what the function returns
