how to use session in asp log in page?

In the login page you can create a session after checking the user has provided the correct username and pasword

Session["username"] = txt_username.Text;
Session["password"] = txt_password.Text;

There after in every page you need to check if the user has been logged in or not , you can do this by checking the session values. So write the following code in every page load event which only logged in users should see.

if(Session["username"] == null || Session["password"]== null)
{
Response.Redirect("Login.aspx");
}
else
{
// You can write your desired code here

}

This is just a small example for lgin process. You should implement proper methods to avoid security breaches like SQL injection and others.

Hope this will help you out.

Let me know in case of any doubts.

Will suggest you to Read this article first
Exploring Session in ASP.Net[^]. This will give you enough idea about ASP.NET Session. After that if you have any question do let us know.

SqlDataAdapter da = new SqlDataAdapter("select * from strUserregistration where strusername='" + txtusername .Text + "' and strpassword= '" + txtpassword.Text + "'", (SqlConnection)Application.Get("con"));
        DataSet ds = new DataSet();
        da.Fill(ds);
        Session["UserName"] = txtusername.Text;
        if (ds.Tables[0].Rows.Count > 0)
        {
            string strname = ds.Tables[0].Rows[0][2].ToString();
            string strtype = ds.Tables[0].Rows[0][13].ToString();

            if (strtype == "Active")
            {
                Response.Redirect("somepage.aspx");
            }
            else
            {
                lblmessage.Text = "Incorrect UserName or Password.";In Inactive ";
            }
        }

Execute this code