ASP.Net MVC: How data is serialize into model when pass to client side from action

I am sending list of data from action to client side. in client side i am binding jquery data table with pass data. column name is extracted because column is dynamic in my case. i got a below code which is not very clear how it is working.

My question is very basic question. see how list of data is pass from action to client side.

[HttpGet]public ActionResult Index()
{

    List<UserData> data = new List<UserData>
    {new UserData
    {
    ID = 1,
    Name = "Simon"
    },new UserData
    {
    ID = 2,
    Name = "Alex"
    }
    };return View(data);
}

passed model data is captured like below way which is not clear to me

var keys = Object.keys(@Html.Raw(Json.Encode(Model[0])));var columns = keys.map(function (key) {return { title: key };
});var data = @Html.Raw(Json.Encode(Model));var dataSet = data.map(function (d) {returnObject.values(d);
});

console.log(columns);
console.log(dataSet);

see this code first

var keys = Object.keys(@Html.Raw(Json.Encode(Model[0])));var columns = keys.map(function (key) {return { title: key };
});

1) we know list is kind of array then why keys are extracted from zeroth position ? Model[0] why not Model[1]

i like to know in what form data is stored into model when pass from action to client side ?
see this code again

var data = @Html.Raw(Json.Encode(Model));var dataSet = data.map(function (d) {returnObject.values(d);
});

2) in above code no ordinal position mention during extracting data. why?

3) what is Model[0] ? how it comes? because in asp.net mvc we write model like @model not Model

4) is this Model is Asp.Net MVC related model or javascript Model object ?

During keys extraction ordinal position is mentioned but in case of data extraction no ordinal position mentioned. please explain if some one understand what i am trying to know.

My main question is i have only one question that what is Model[0] here in js? is it any JavaScript related object or server side object ? if it is javascript then how server side model data comes into js model ?

please explain how above code is working at client side. thanks