Unhiding a column is usually pretty easy. All you do is select the column header to the right and to the left of the hidden column and then right-click and select Unhide.
In the example below, Column B is hidden so I selected across the Column A header and Column C header (which means that Column B was also included) and then selected Unhide from the shortcut menu.
Unhiding is a little more difficult when you have hidden Column A. To unhide Column A you need to go to the Name Box located above Column A and B and type A1.
Then press Enter.
This forces Excel to put the cursor into cell A1. At that point, you can right-click and select Unhide. It may look like nothing happened but Excel did unhide it. Excel tends to keep the width so small that you may still not be able to actually see Column A even though it is unhidden. If that is the case, move your cursor carefully until you get the cursor to look like a 4 headed cross which will allow you to widen Column A.