How does one connect to Oracle from VB?

Connectivity to Oracle is provided via ODBC or OO4O (Oracle Objects for OLE). For more information about ODBC, read the ODBC FAQ. For information about OO4O, read the OO4O FAQ. Look at this examples:

' DAO Example (Data Access Objects)

Dim wstemp As Workspace
Dim dbtemp As Database
Dim rstemp As Recordset

Set wstemp = DBEngine.Workspaces(0)
Set dbtemp = wstemp.OpenDatabase("", False, False, "ODBC;DSN=Oracle;USR=scott;PWD=tiger")
Set rstemp = dbtemp.OpenRecordset(myquery.Text, dbOpenDynaset, dbSQLPassThrough)
howmany = 0
Combo1.Clear
Do Until rstemp.EOF
 	msgbox rstemp(0)
	rstemp.MoveNext
	howmany = howmany + 1
Loop

' RDO Example (Remote Data Objects)

Dim contemp As New rdoConnection
Dim rstemp  As rdoResultset
Dim envtemp As rdoEnvironment
Set envtemp = rdoEngine.rdoEnvironments(0)
envtemp.CursorDriver = rdUseServer
	          ' or rdUseOdbc, rdUseNone, rdUseIfNeeded, rdUseClientBatch
With contemp
  .Connect = "ODBC;DSN=Oracle;USR=scott;PWD=tiger"
  .EstablishConnection rdDriverNoPrompt, false, rdoForwardOnly
                                           ' or rdoStatic, rdoKeyset, rdoDynamic
End With

Set rstemp = contemp.OpenResultset("select ...") ' Your SQL here

howmany = 0
With rstemp
Do Until .EOF Or howmany > 2000
   msgbox .rdoColumns(0) ' Popup a message box showing the 1st column
   .MoveNext
   howmany = howmany + 1
Loop

ADO Example

Option Explicit

Public m_adoCnn As New ADODB.Connection
Public m_adoRst As New ADODB.Recordset

Public Sub Command1_Click()
    m_adoCnn.ConnectionString = "Provider=MSDAORA;Password=tiger;User ID=scott;Data Source=database"
    m_adoCnn.Open
End Sub

Private Sub Form_Unload(Cancel As Integer)
    m_adoCnn.Close
End Sub

OO4O Example

Option Explicit

Dim m_oraSession  As Object
Dim m_oraDatabase As Object

Private Sub Command1_Click()
    Set m_oraSession = CreateObject("OracleInProcServer.XOraSession")
    Set m_oraDatabase = m_oraSession.DBOpenDatabase("Database", "user/password", 0&)
    
    MsgBox "Connected to " & m_oraDatabase.Connect & "@" & m_oraDatabase.DatabaseName
End Sub

Private Sub Form_Unload(Cancel As Integer)
    Set m_oraDatabase = Nothing
    Set m_oraSession = Nothing
End Sub