Display Menu and SubMenu Items

I’m not sure if this can be done w/o a plugin, but I figured I would ask the experts…

I have a menu structure as follows… Item1, Item2, Item3, &c.

Under each ItemX are 4-7 submenu items… SubItem1, WsubItem2, SubItem3, &c.

What I want to do is show the list of SubItemX in the sidebar of the page ItemX takes you to.

So, click on About, and the sidebar is populated with About-Sub-1, About-Sub-2, About-Sub-3, &c.

Click on Training, and get Training-Sub-1, Training-Sub-2, Training-Sub-3, &c.

If I am way off base here, and a plugin is require, could you recommend one?

Thanks… Jeff