Gostinitsa/Menu.cs

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

namespace Khozeev8
{
    public partial class Menu : Form
    {
        Database database = new Database();
        public Menu()
        {
            InitializeComponent();
            StartPosition = FormStartPosition.CenterScreen;
        }

        private void Menu_Load(object sender, EventArgs e)
        {

        }

        private void button1_Click(object sender, EventArgs e)
        {
            var Name = textBox1.Text;
            var Colvo = textBox2.Text;
            var Type = textBox3.Text;
            var Cost = textBox4.Text;

            string querystring = $"insert into Комплектующие(Наименование, Количество,ТипДетали,Цена) values ('{Name}' , '{Colvo}', '{Type}','{Cost}')";

            SqlCommand command = new SqlCommand(querystring, database.GetConnection());

        }

        private void button2_Click(object sender, EventArgs e)
        {
            Aithorization frm = new Aithorization();
            this.Hide();
            frm.Show();
        }
    }
}