using (SqlConnection conn = new SqlConnection(sqlConString))
{
    SqlCommand insertQuery = new SqlCommand("INSERT INTO user_table (Username, Password, Name, Surname, DOB) VALUES ( @0, @1, @2, @3, @4 )", conn);

    insertQuery.Parameters["@0"].Value = edtUsername.Text;
    insertQuery.Parameters.AddWithValue("@1", edtPassword.Text);
    insertQuery.Parameters.AddWithValue("@2", edtName.Text);
    insertQuery.Parameters.AddWithValue("@3", edtSurname.Text);
    insertQuery.Parameters.AddWithValue("@4", dateTimePicker.Text);

    conn.Open();
    insertQuery.ExecuteNonQuery();
    conn.Close();
} // using conn

using (var conn = new SqlConnection(sqlConString))
{
    using(var insertQuery = new SqlCommand("INSERT INTO user_table (Username, Password, Name, Surname, DOB) VALUES ( @Username, @Password, @Name, @Surname, @DOB)", conn))
    {
        // I'm assuming nvarchar as the data type, change it if needed....
        insertQuery.Parameters.Add("@Username", SqlDbType.NVarChar).Value = edtUsername.Text;
        // uniqueSalt can be stored as plain text in the database, but should be unique for each password.
        insertQuery.Parameters.Add("@Password", SqlDbType.NVarChar).Value = HashPassword(edtPassword.Text, uniqueSalt);
        insertQuery.Parameters.Add("@Name", SqlDbType.NVarChar).Value = edtName.Text;
        insertQuery.Parameters.Add("@Surname", SqlDbType.NVarChar).Value = edtSurname.Text;
        insertQuery.Parameters.Add("@DOB", SqlDbType.DateTime).Value = dateTimePicker.Value;
        conn.Open();
        insertQuery.ExecuteNonQuery();
    }
}

string HashPassword(string password, string salt)
{
    // TODO: Implement hashing with salt
}