Hi Sugada,
Fairly simple ... After you have hidden the columns, use Tools, Protection, Protect Sheet. In this window, there will be a position for entry of a password. Naturally, you will want to ensure that you do not forget or misplace your filed hard-copy of the password. Otherwise, you will be unable to later unprotect the sheet.
Another important point to appreciate... When you protect the sheet, ALL cells immediately become protected - unless cells or ranges of cells, or columns, or rows, have been previously "unlocked".
When you choose Format, Cells, Protection (from the menu), you will notice that all cells initially have a check-mark opposite "Locked". But this "Locked" format ONLY becomes active once the Sheet is Protected (with Tools, Protection, Protect Sheet).
Therefore, what you will want (need) to do PRIOR to protecting the sheet, is to format all those cells where you will want to give access to the end-user regarding editing or entering data. Depending upon your application, THIS part can be more of a challenge - i.e. to disable "Locked" for all those cells/ranges where the user will need to have access.
Hope this helps.
Regards, ...Dale Watson dwatson@bsi.gov.mb.ca