DBNameDataContext myDataBase = new DBNameDataContext();
    var userResults = from u in myDataBase.Users
                         where u.Username == userName
                         && u.Password == passWord
                         select u;
    return Enumerable.Count(userResults) > 0;

 DBNameDataContext Mydatabase = new DBNameDataContext();

            var q = from c in Mydatabase.Contact
                    where c.UserDateOfBirth.AddYears(35) > DateTime.Now
                    orderby c.UserDateOfBirth descending
                    select c;

            foreach (var c in q)
                Console.WriteLine("{0} {1} b.{2}",
                            c.FirstName.Trim(),
                            c.LastName.Trim(), c.UserDateOfBirth.ToString("dd-MMM-yyyy"));

using (NorthwindDataContext db = new NorthwindDataContext())
{
    var q = from c in db.Customers
            where c.City == "London"
            select c;
}