Submenu only visible on specific page

Hi,

I have this menu, where each item has its children, structure:

• Item #1

• Subitem #1

• Item #2

• Subitem #2
• Subitem #3

• Item #3

What I want to do is: when I’ m on the homepage, I only want to see the main menu (Item #1 > 3). But when I click one of these items, I’ d like to see the subitems displayed in the page itself, underneath the main menu- items.
So for example I click Item #2, then I want to see Subitems #2 and #3 and none of the other subitems.

Anyone who can help me, or provide a link where I can find more information about this topic?