You can return an anonymous object from your function

public static object FunctionWithUnknowReturnValues ()
{
    /// anonymous object
    return new { a = 1, b = 2 };
}

And assign the result to a dynamic object and read the values in it.

/// dynamic object
dynamic x = FunctionWithUnknowReturnValues();

Console.WriteLine(x.a);
Console.WriteLine(x.b);

You can return an instance of Tuple class from your function with two template parameters as Tuple<string, MyClass>:

public Tuple<string, MyClass> FunctionWith2ReturnValues ()
{
    return Tuple.Create("abc", new MyClass());
}

And read the values like below:

Console.WriteLine(x.Item1);
Console.WriteLine(x.Item2);

The ref keyword is used to pass an Argument as Reference (opens new window). out will do the same as ref but it does not require an assigned value by the caller prior to calling the function.

Ref Parameter :-If you want to pass a variable as ref parameter then you need to initialize it before you pass it as ref parameter to method.

Out Parameter :- If you want to pass a variable as out parameter you don’t need to initialize it before you pass it as out parameter to method.

static void Main(string[] args)
{
    int a = 2;
    int b = 3;
    int add = 0;
    int mult= 0;
    AddOrMult(a, b, ref add, ref mult); //AddOrMult(a, b, out add, out mult);
    Console.WriteLine(add); //5
    Console.WriteLine(mult); //6
}

private static void AddOrMult(int a, int b, ref int add, ref int mult) //AddOrMult(int a, int b, out int add, out int mult)
{
    add = a + b;
    mult = a * b;
}

Remarks

There is no inherent answer in C# to this - so called - need. Nonetheless there are workarounds to satisfy this need.

The reason I qualify the need as "so called" is that we only need methods with 2 or more than 2 values to return when we violate good programming principals. Especially the Single Responsibility Principle (opens new window).

Hence, it would be better to be alerted when we need functions returning 2 or more values, and improve our design.