How do I pass textbox\input values from view to controller in MVC

If you want to keep your controller action and view the same you can simply add the name property to match your action parameters and they will pass the data across:

<input type="text" class="textbox" id="username" name="username">
<input type="password" class="password" id="password" name="password">

However I would recommend using strongly typed view models as there is less room for error and makes better use of the framework.

In order to do this you would do the following:

Create a class that holds your properties and add DisplayName attributes for your labels:

public class FooViewModel 
{
   [DisplayName("Username")]
   public string Username { get; set; }
   [DisplayName("Password")]
   public string Password { get; set; }
}

Add a model directive to your view and use HtmlHelpers instead of html inputs:

@model FooViewModel
<div>
    <span>@Html.LabelFor(x => x.Username)</span>
    <span>@Html.TextBoxFor(m=> m.Username)</span>
</div>
<div>
    <span>@Html.LabelFor(x => x.Password)</span>
    <span>@Html.PasswordFor(m=> m.Password)</span>
</div>

Then change your action to this:

public ActionResult LoginMethod(FooViewModel model)
{
   if (model.Username == "admin" && model.Password == "admin1")
   {
     return RedirectToAction("Home");
   }
  else 
  {
     return RedirectToAction("Login");
  }
}

Generally it is better to use a viewmodel to post the data back to, this also lets you do some validation.

So you define a model:

public class MyViewModel
{
    [Required]
    [StringLength(50)]
    [Display(Name = "Username")]
    public string Username { get; set; }

    [Required]
    [StringLength(50)]
    [Display(Name = "Password")]
    public string Passsword { get; set; }
} 

So your markup becomes:

@model MyViewModel
@using(Html.BeginForm())
{
    <div>
        <span>@Html.LabelFor(m => m.Username)</span>
        <span>@Html.TexboxFor(m => m.Username)</span>
        Html.ValidationMessageFor(x => x.Username)
    </div>
    <div>
         <span>@Html.LabelFor(m => m.Password)</span>
         <span>@Html.PasswordFor(m => m.Password)</span>
         Html.ValidationMessageFor(x => x.Password)
    </div>
}

And you controller action is:

public ActionResult LoginMethod(MyViewModel myViewModel)
{
    if (myViewModel.Username == "admin" && myViewModel.Password == "admin1")
    {
        return RedirectToAction("Home");
    }
    else return RedirectToAction("Login");
}

You can get it to work by setting the name attribute to match the parameters to the action, or the properties of the viewmodel but using a viewmodel and helpers is much more robust and easier to refactor, plus validation.

First you should put your inputs in a form like,

<% Html.BeginForm("LoginMethod", "Authentication");%>
  Username: <input type="text" id="username" name="username"  />
  Password: <input type="password" id="password" name="password"  />
  <input type="submit" id="Go" value="Post" />
<% Html.EndForm();%>

or you can use <%: Html.TextBoxFor(m => m.UserName) %> instead of html inputs.

and here your Controller method;

public ActionResult LoginMethod(string username,string password)
{ 
   **do your stuff!
}