To make some column and rows wider or thinner, place the mouse on the border between the columns or rows and drag the mouse to make it the size you want.
You can also apply this to many rows or columns. By selecting them first (press on the D or C for example) then going to one intersection (between C and D for example), you can adjust at will.
Tip: What is selected can also be formatted in the style you want. Just apply the styles or formats (see previous chapters)