Inserting blank cells in Numbers like Excel

I just imported an Excel spreadsheet that covers expenses for 12 months with 5 columns/month. To do what I have done in Excel I require the insert cell command (or equivalent) for blank cells in selected monthly columns. I need to insert blank cells pushing items below the insert point down. Easy and very routine in Excel but I see no way in Numbers. Without this ability it is back to "Excel '08 for Mac".