You can change the column widths in Excel using the mouse. For example if I want to change the column width of column A.

Place the mouse cursor on the line between column A and column B

The mouse cursor will change to a double-headed arrow.

Double left click with the mouse button and the column will auto adjust.

Note: You can also manually adjust the length of a column. Instead of double clicking with the left mouse button, click the left mouse button once and drag to change the width accordingly.