In the Article previous, I say to TagHelper in ASP.NET Core 2.1, in this article I share more information about this library.
You can see again the article previous: Create Project ASP.NET Core 2.1
The Tag Helper is a library help insert URL in element , In ASP.NET MVC 5 you can call URL @Url.Action(). But in ASP.NET Core 2.1 we use simple more much
You can see it : https://docs.microsoft.com/en-us/aspnet/core/mvc/views/tag-helpers/intro?view=aspnetcore-2.1

<ul class="nav navbar-nav">
                    <li><a asp-area="" asp-controller="Home" asp-action="Index">Home</a></li>
                    <li><a asp-area="" asp-controller="Home" asp-action="About">About</a></li>
                    <li><a asp-area="" asp-controller="Home" asp-action="Contact">Contact</a></li>
                    <li><a asp-area="" asp-controller="Home" asp-action="Detail" asp-route-id="2">Detail</a></li>
                    <li><a asp-area="" asp-controller="Home" asp-action="Product" asp-all-route-data="parms">Product</a></li>
                    <li><a asp-route="ProductCategory" asp-all-route-data="parms">Product2</a></li>
  </ul>

asp-controller="Home" : we call HomeControler.cs file in Controllers folder
asp-action="Index" : call action "Index" in HomeController.cs file
asp-route-id="2": use insert params to Index(int? id){}, example: https://localhost:44348/Home/Detail/2
asp-all-route-data: use insert params(Key,value), example: https://localhost:44348/Home/Proudct?ProductID=11&CategoryID=4

Example: ProductID=2, CategoryID=4

  //HomeController.cs
  [Route("/Home/Product",
         Name = "ProductCategory")]
  public IActionResult Product(int ProductId,int CategoryId)
  {
       return View();
  }

You can use it the following code below

  @{
  var parms = new Dictionary<string, string>
              {
                  { "ProductID", "11" },
                  { "CategoryID", "4" }
              };
  }
  <a asp-controller="Home" asp-action="Product" asp-all-route-data="parms">Product</a>
  //or
  <a asp-route="ProductCategory" asp-all-route-data="parms">Product</a>

Through this article you can imagine , we use Tag Helper call URL, insert params to URL
The Article : Anchor Tag Helper in ASP.NET Core 2.1