Login Code

First i think you need to create a new database, then run the sql script as below to create a user table

CREATE TABLE [dbo].[Users](
    [UserName] [varchar](25) NOT NULL,
    [Password] [varchar](50) NULL,
 CONSTRAINT [PK_Users] PRIMARY KEY CLUSTERED 
(
    [UserName] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

Now, create a new windows forms project, then design your login form as below, you can design a beautiful login form

OK, that's time we use entity framework to check login

Right click on your project, then select Add New Item

Select ADO.Net Entity Data Model and put your name is Model

The next screen we select EF Designer from database

You need to enter account information to connect to your sql database

Select include the connectionstring in app.config file, then enter with name is DbEntites

The next screen you can select the version entity framework that you want to use, then click next button

Select User table, then enter your model namespace is DbModel and click Finish

Now, Open your login form and double click on the login button to add event handle code to login form

private void btnLogin_Click(object sender, EventArgs e)
{
    using (DbEntities db = new DbEntities())
    {
        var query = from u in db.Users
                    where u.UserName == txtUserName.Text && u.Password == txtPassword.Text
                    select u;
        if (query.SingleOrDefault() != null)
            MessageBox.Show("Login succesfull !");
        else
            MessageBox.Show("Login fail !");
    }
}

You can use LinQ to check user login. Now, Open your user table then insert some data to play demo