How to show submenus items of the main menu in Drupal 7 sites

The problem

Don't you see the secondary choises of Main Menu in your website developed in Drupal 7?

What to check

The first thing to check is the configuration of the Main links and Secondary links of the site.

The links above are configured at admin/structure/menu/settings' URL. And to display the submenus of theMain Menu, this one must be the source *as inMain linksas inSecondary links`*.

After that, you must to be sure that are correctly configured the submenu items. There are at least a couple of ways to do it.

The first one is the easiest to use when creating new contents. In this case, before saving the new content, you must:

Check the box provide a menu link in the tab menu settings;
Write a link title (often the one proposed by default Drupal is acceptable);
Select the parent item, that is: what menu, or what upper choise, this new link will belong;
Make any other decision relating to the content (eg. Comment Settings and/or publishing options);
Finally save it.

The second way is easier reviewing the overall structure of the site. It operates at the admin/structure/menu/manage/main-menu URL. This address shows the list of items in the Main Menu, allowing visually to verify which entry is primary and which is instead a secondary link. In this same window you can change the organization of the menu by modifying the weights (order of appearance) and the configuration of each item and/or subitem that compose it.

Another check

Make attention if you have more main menu items linking to the same base page.

Working with Drupal 7 in thi condition, I have observed submenus malfunctions. So now I prefer to link to a base page using only one main menu voice.