A double-backed arrow indicates that you can change a cell edge.
Once you've added columns or rows, you may decide that a column needs to be wider or narrower, especially if one of the AutoFit options doesn't do the trick.
The easiest way to change the width or height of a column or row is to rest the pointer over the right edge of the column or the bottom edge of the row until your pointer changes to a double-backed arrow, as shown in the illustration. Then just click and drag to resize.
Be careful: If you select a single cell, only that cell will change size.
If your table doesn't have borders, you might have trouble seeing the edges of the cells. Gridlines allow you to easily see cell edges. To turn on gridlines, click anywhere within the table, and then click View Gridlines in the Table group of the Layout tab.
You'll get a chance to resize your table columns in the practice, which is next.