aaaa/ad/Form1.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace ad
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            SqlConnection connection = new SqlConnection("Data Source=CLASS3108;Initial Catalog=konkurstest;Integrated Security=True");


            SqlCommand command = new SqlCommand("SELECT * FROM users WHERE password=@password AND login =@login ", connection);
            command.Parameters.Add("@password", textBox1.Text);
            command.Parameters.Add("@login", textBox2.Text);

            SqlDataReader read = null;
            connection.Open();
            try
            {
                read = command.ExecuteReader();

                    read.Read();
              
                    if (read["admin"].ToString() == "1")
                    {
                        Form2 f2 = new Form2();
                        f2.Show();
                        this.Hide();
                    }
                    if (read["manager"].ToString() == "1")
                    {
                        Form3 f3 = new Form3();
                        f3.Show();
                        this.Hide();
                    }


            }
            catch(Exception ex)
            {
                MessageBox.Show(ex.Message.ToString(), "",MessageBoxButtons.OK, MessageBoxIcon.Error);
            }

        }
    }
}