All cell formatting options are under the 'Format' menu option.

There is an option here for example Format>Column>Width... this shows a
dialog to specify the width in 'fixed width' characters for the selected
column(s).

You can also select 'Auto-fit' from here.  This will size the column(s) to
the width of the widest entry.

You can also, as a quick 'auto-fit', double-click to the right of the column
header.  (Where it joins the column header to the right. You're in the right
place when the cursor changes to an 'East-West' arrow)