Excel will insert new columns to the left of the selected columns. The keyboard shortcut for this task is also Ctrl + Shift + +. This works with multiple rows but not non-contiguous selections.

sometimes abbreviated as CTRL) or the Command Key (on MacOS machines, sometimes abbreviated as CMD) in various ways to make the magic happen. Other keys typically involved in keyboard shortcuts ...

Here's a list of CTRL keyboard shortcuts for Microsoft Excel 2010.