How to write to database using Linq-to-SQL

/// <summary>
/// GetAllCarts
/// Sends all carts in database to list
/// </summary>
[OperationContract]
List<Lloyds_Cart> GetAllCarts()
{
    PositionDataClassesDataContext context = new PositionDataClassesDataContext();

    var res = from carts in context.Lloyds_Carts select carts;

    return res.ToList();

}
/// <summary>
/// Create a new Cart
/// </summary>
[OperationContract]
void CreateCart()
{
    PositionDataClassesDataContext context = new PositionDataClassesDataContext();
}