Q:

How to display elements of list from controller to view [MVC5]

I have function in controller: 
public ActionResult Add(string id_klasy)
{
    var dataContext = db.Uczniowie;
    List<string> ucz = new List<string>();
    var uczniowiee = dataContext.Where(m => m.KlasaId.Equals(id_klasy));
    ucz = uczniowiee.Select(m => m.Nazwisko + " " + m.Imie).ToList();
    return View(ucz);
}

I want show data to view 

A:

You could try something as simple as this:
@model IEnumerable<string>

<ul>
@foreach(var name in Model)
{
    <li>@name</li>
}
</ul>

This is the code you have to place in your view. Your view has as a model a sequence of strings. You simple loop through this sequence and you create for each of them an li element.
The view can be added very easily by going on the ActionResult method's name and right click of the mouse. Then select Add View.
As a side note, I would suggest to refactor the code in your controller to the following one:
public ActionResult Add(string id_klasy)
{
    var dataContext = db.Uczniowie;
    var ucz = dataContext.Where(m => m.KlasaId.Equals(id_klasy))
                         .Select(m => m.Nazwisko + " " + m.Imie);
    return View(ucz);
}

I think that this is a more compact way to achieve that you want.

