This method is the same as that used in Excel®. Hover the mouse over the line dividing the column name; the mouse pointer changes from an arrow to a cross shape. Click and hold as you slide the vertical line left or right. To adjust the column so that it fits the size of the data, double-click the cross.
If you widen the right-most column toward the right, you may need to use the horizontal scroll bar to see the full column width.