I want to send to a list of email addresses in my workbook.
How would I go about that with what I have for the mailing section of my code?
I want to have column R named mailing list and it will send to whatever email addresses are inserted into that column/list all together.
Sub SendReminderMail1()
Dim wb1 As Workbook
Dim wb2 As Workbook
Dim TempFilePath As String
Dim TempFileName As String
Dim FileExtStr As String
Dim OutApp As Object
Dim OutMail As Object
With Application
.ScreenUpdating = False
.EnableEvents = False
End With
Set wb1 = ActiveWorkbook
TempFilePath = Environ$("temp") & "\"
TempFileName = "Copy of " & wb1.Name & " " & Format(Now, "dd-mmm-yy h-mm-ss")
FileExtStr = "." & LCase(Right(wb1.Name, Len(wb1.Name) - InStrRev(wb1.Name, ".", , 1)))
wb1.SaveCopyAs TempFilePath & TempFileName & FileExtStr
Set wb2 = Workbooks.Open(TempFilePath & TempFileName & FileExtStr)
wb2.Worksheets(1).Range("A1").Value = "Copy created on " & Format(Date, "dd-mmm-yyyy")
wb2.Save
Set OutApp = CreateObject("Outlook.Application")
Set OutMail = OutApp.CreateItem(0)
On Error Resume Next
With OutMail
.To = " "
.CC = ""
.BCC = ""
.Subject = "Rotations needed for ."
.Body = "Hey there, equipment needs to be rotated."
.Attachments.Add wb2.FullName
.Display 'or use .Send to send with display proof reading
End With
On Error GoTo 0
wb2.Close savechanges:=False
Kill TempFilePath & TempFileName & FileExtStr
Set OutMail = Nothing
Set OutApp = Nothing
With Application
.ScreenUpdating = True
.EnableEvents = True
End With
MsgBox "Your Automated Email for BP Rotations was successfully ran at " & TimeValue(Now), vbInformation
End Sub

In your code I've you set the recipients fields to empty strings:
Instead, you need to read values from the column R and add recipients for the email. To add recipients I'd recommend using the
Recipientscollection which can be retrieved using the corresponding property of theMailItemclass.Read more about that in the How To: Fill TO,CC and BCC fields in Outlook programmatically article.