combine two columns across sheets in one column

Alaa

The attached file contains the revised macro below (heavily commented for your guidance)- it can now be run from a form button called "Collate from other sheets" on the "summary" sheet.

It uses a VBA dictionary (which is alphabetically sorted anyway) whose "key" is the combined values (from columns B and C) and the output (currently blank) will list the combinations plus say where they were found (in column D) - I think that might be useful when you have many rows but you could change the code to avoid that.

To understand a little more about why I used a dictionary, see my recently selected Answer at higlight new data across sheets with matching in another

Note there's a (commented) line in bold below giving you an extra learning point.

Sub CopyRange()
    Dim bottomB As Integer
    Dim ws As Worksheet
    Dim OutDict As Object, Key As Variant, n As Integer, Val As String
    'create a new empty dicionary
    Set OutDict = CreateObject("scripting.dictionary")

    'Loop through sheets
    For Each ws In Sheets(Array("A", "B", "C"))
        'ws.Activate ' ## no need to activate a worksheet to work on it
        bottomB = ws.Range("B" & Rows.Count).End(xlUp).Row
        ' loop down sheet rows
        For n = 2 To bottomB
            'create a "key" from B and C with a rare delimiter (¬)
            Val = ws.Cells(n, 2) & "¬" & ws.Cells(n, 3)
            ' if there's no dictionary key like that, add one with no value
            If Not OutDict.exists(Val) Then OutDict.Add Key:=Val, Item:=""
            ' add something to the value for that key (here the worksheet name and cell without $ signs)
            OutDict(Val) = OutDict(Val) & ws.Name & "(" & Cells(n, 2).Address(False, False) & "); "
        Next n
    Next ws

    With Sheets("summary")
        bottomB = .UsedRange.Rows.Count
        'clear existing rows below header (if any)
        If bottomB > 1 Then .Range("B2:B" & bottomB).EntireRow.Delete
        n = 2
        ' loop through dictionary and add to row (n)
        For Each Key In OutDict
            'split values (using delimter ¬), add to cells and draw borders
            .Cells(n, 2).Resize(1, 2) = Split(Key, "¬")
            'optionally output the dictionary value
            .Cells(n, 4) = OutDict(Key)
            'draw borders around cells
            .Cells(n, 2).Resize(1, 3).Borders.LineStyle = xlContinuous
            'increment row counter
            n = n + 1
        Next Key
        ' set the column widths to suit contents
        .Columns("B:D").AutoFit
        ' show this sheet
        .Activate
    End With
    ' tell user something happened
    MsgBox "Items found= " & OutDict.Count
End Sub

Finally, you're using an array of sheet names for your loop- that's fine but if you have just one summary sheet and need to loop through every other sheet (and there are many more than 3), you might want to use this instead (same code extract as above but with changes in bold and comments removed):

    'Loop through sheets
    For Each ws In ThisWorkbook.Sheets
        If ws.Name <> "summary" Then
        bottomB = ws.Range("B" & Rows.Count).End(xlUp).Row
            For n = 2 To bottomB
                Val = ws.Cells(n, 2) & "¬" & ws.Cells(n, 3)
                If Not OutDict.exists(Val) Then OutDict.Add Key:=Val, Item:=""
                OutDict(Val) = OutDict(Val) & ws.Name & "(" & Cells(n, 2).Address(False, False) & "); "
            Next n
        End If
    Next ws

Hope this helps.