ExecuteScalar sql

Dim conex As String =""
Dim con As New SqlConnection(conex)
Try
Dim query As String=""
con.Open()
 Using cmd As New SqlCommand(query, con)
                cmd.Parameters.Add("@id", SqlDbType.Int).Value = TextBox.Text
                id_adjunto_IN = cmd.ExecuteScalar()
            End Using
con.Close()
Catch ex As Exception
con.close()
End Try

Ejecutar procedimiento almacenado con using

Dim con As New SqlConnection(conex)

con.Open()
Using cmd As New SqlCommand("SP_nombre_sp", con)
        cmd.CommandType = CommandType.StoredProcedure
        cmd.Parameters.Add("@rut", SqlDbType.VarChar).Value = rut.
        cmd.Parameters.Add("@usuario", SqlDbType.VarChar).Value = usuario.
        cmd.Parameters.Add("@clave", SqlDbType.VarChar).Value = clave
        resp = cmd.ExecuteScalar()
End Using
con.Close()

Otra opción

 con.Open()
 Dim cmd As System.Data.SqlClient.SqlCommand = Nothing
 cmd = New System.Data.SqlClient.SqlCommand("SP_nombre_sp", con)
 cmd.Parameters.Add("@rut", SqlDbType.VarChar).Value = rut.Trim
 cmd.Parameters.Add("@usuario", SqlDbType.VarChar).Value = usuario
 cmd.Parameters.Add("@clave", SqlDbType.VarChar).Value = clave
 cmd.CommandType = CommandType.StoredProcedure
 resp = cmd.ExecuteScalar()
 con.Close()

Leer tabla sql

Dim query As String = "SELECT * FROM tabla"
        Try
            Dim con As New SqlConnection(conex)
            con.Open()
            Dim cmd As New SqlCommand(query, con)
            Dim dr As SqlDataReader = cmd.ExecuteReader()
            While dr.Read
                Dim id As String = dr.GetValue(0).ToString.Trim
                Dim name As String = dr.GetValue(1).ToString.Trim
                Dim code As String = dr.GetValue(2).ToString.Trim
                
            End While
            dr.Close()
            con.Close()
        Catch ex As Exception
        End Try