Select the column or columns you want to resize
Place the cursor on the right border of the column header until it turns into a double-headed arrow
Click and drag the border left or right to adjust the width
Double-click the right border to AutoFit the column width to the contents
Right-click the selected column header and choose Column Width
Enter the desired width and click OK
Use the Home tab, then select Format in the Cells group, then choose Column Width
Drag the boundary between column headers to resize multiple columns at once
Select the entire sheet and use AutoFit Column Width to adjust all columns at once