Tung,
Samples of how to add a button to the existing toolbar are included in the BO SDK.
Typically, the buttons are added via a routine included in an established REA file (add-in file). You must determine the indexes used by the existing toolbars to determine what the next available index number will be.
A sample of a adding a button to a toolbar is as follows:
Sub Add_BCA_Email_to_Menu()
Set BO_CmdbarControl = Application.CmdBars.Item(1).Controls.Item("&Tools"

.Controls.Add(1, , 15)
BO_CmdbarControl.Caption = "A&ttach to Email..."
BO_CmdbarControl.OnAction = ThisDocument.Name & Right(ThisDocument.FullName, 4) & "!InsertCode"
Application.Clipboard.SetData LoadPicture(ThisDocument.Path & "\mail.bmp"

BO_CmdbarControl.PasteFace
Set BO_CmdbarControl = Application.CmdBars.Item(2).Controls.Item("&Tools"

.Controls.Add(1, , 15)
BO_CmdbarControl.Caption = "A&ttach to Email..."
BO_CmdbarControl.OnAction = ThisDocument.Name & Right(ThisDocument.FullName, 4) & "!InsertCode"
Application.Clipboard.SetData LoadPicture(ThisDocument.Path & "\mail.bmp"

BO_CmdbarControl.PasteFace
Set BO_CmdbarControl = Application.CmdBars.Item(5).Controls.Add(boControlButton, , 24)
BO_CmdbarControl.Caption = "A&ttach to Email..."
BO_CmdbarControl.OnAction = ThisDocument.Name & Right(ThisDocument.FullName, 4) & "!InsertCode"
Application.Clipboard.SetData LoadPicture(ThisDocument.Path & "\mail.bmp"

BO_CmdbarControl.PasteFace
Application.CmdBars("Standard"

.Controls(25).Caption = "Attach BCA Documents to EMail"
Application.CmdBars("Standard"

.Controls(25).TooltipText = "Attach BCA Documents to EMail"
Application.CmdBars("Standard"

.Controls(25).DescriptionText = "Attach BCA Documents to EMail"
End Sub
This sub routine is called on the Document_Open event
Private Sub Document_Open()
Call Add_BCA_Email_to_Menu
End Sub
You must also have a bitmap file to paste onto the toolbar button, and an established sub or function to call upon pressing the button.