If Not Evaluate code

Hello. What does this code mean? Could someone walk me through the syntax?

  If Not Evaluate("ISREF('" & cell.Value & "'!A1)") Then
        Sheets.Add(after:=Sheets(Sheets.Count)).Name = cell.Value
    Else
        Sheets(CStr(cell.Value)).UsedRange.ClearContents
        Sheets(CStr(cell.Value)).Activate
    End If