Re: Add feature to Menu
Go to the Admin Menus page (tiki-admin_menus.php) and click on the Configure/Options icon (the tools) for the menu you want to modify. I guess by main menu you mean menu 42. Enter the information about the link you want to add in the Edit Menu Options form — its name, URL, section (in other words: Tiki feature) and permission info if necessary. See existing items for the pattern of how menu item information is entered.
Notice that the items are displayed in the menu in the order determined by their position number. Tiki's default menu has (and, I'd recommend, any custom menu should have) unused numbers left between the numbers used for items, so that you can add new items without having to re-number every item below the new one in the menu.
See also the docs page for more information on menus.
-- Gary