LINQ Query to retrieve Data from multiple Database tables

[LisaWvL]

Hey there yet again.

I´m still crushing my teeth at using LINQ in C# correctly..
right now i´m trying to create a view or temporary table to retrieve the data from my 3 tables where The ID == REF_ID.
i know i got to use the JOIN in some way, but don´t really get yet, how to do that.
I got 3 tables
Rezepttabelle (parent table with RezeptID column)
Kategorien (child table with REF_RezeptID column)
Zutaten (child table with REF_RezeptID column)

I want to get all the data joined where REF_RezeptID = RezeptID and display that data in a datagridview on my form1.

        /// <summary>
        /// 
        /// </summary>
        public void Rezept_load()
        {
            //a new connection to the database is created.
            SqlConnection con = new SqlConnection();
            //connection string to the database
            con.ConnectionString =
                     @"Data Source=vm-msdb01\fme;Initial Catalog=Lisa;Persist Security Info=True;User ID=sa;Password=fmefme";
            //connection opened
            con.Open();

            //the values from the various textboxes are added to the main table.
            //the id is created automatically.
            SqlCommand cmd = new SqlCommand("");
            
            try
            {
                cmd.ExecuteNonQuery();
            }

            //any errors occuring are caught here
            catch (SqlException ex)
            {
                throw new Exception(ex.ToString());
            }

            //the connection is closed
            finally
            {
                con.Close();
            }
        }

that´s my code so far, as u can see, the sql query is empty, for i have no idea how to make my statement...
maybe you can help me, i really hope so

Greetings and Cheers

Cheers