Lertap5 is an Excel application. Your computer must be able to run Excel, the spreadsheet program from Microsoft, usually distributed as one of the applications in the software suite called "Microsoft Office". Other applications in this suite are Word, Access, and PowerPoint.
So? Excel. You need it to run Lertap5. Got it? Good. But note: your copy of Excel has got to be one which will "run macros". The version of Excel for the iPad is not capable of running macros. The various "mobile" versions of Excel, handy and powerful as they may be, are not capable of running macros either. (Macros are modules of computer code; Lertap 5 code is written in "VBA", Visual Basic for Applications.)
Do you have a Windows or Macintosh computer using Excel? If not, Lertap5 may not be for you (alas!).