Default the submenus are disabled!
Go to Theme Styles > SubMenu Off|On|Position and SidebarHeader Off|On|Position and choose an option:

When set under the Header, if you have a "third" level page, example: Top Nav-Page 1 / SubMenu-Page 2 / SubMenu Sub-Page 3, it doesn't show. Only when the SubMenu is in the SideBar.
• BOHEMIAN Split (example: this page)

BOHEMIAN Split has a SplitMenu: only the sublevel(s) of the current topmenu show up. The first level of navigation is always horizontal and displays at the top of the page.
For second level navigation, you decide if you'd prefer it vertically in the sidebar (this choice allows for further sub-levels of navigation, see image left) or horizontally below the header image (this choice is limited to two levels of navigation, see image right).
For second level navigation, you decide if you'd prefer it vertically in the sidebar (this choice allows for further sub-levels of navigation, see image left) or horizontally below the header image (this choice is limited to two levels of navigation, see image right).
• BOHEMIAN Dual (example this page)

BOHEMIAN Dual has a DualMenu: all sublevels show up. The first level of navigation is always horizontal and displays at the top of the page.
For second level navigation, you decide if you'd prefer it vertically in the sidebar. This choice allows for further sub-levels of navigation (see image left), or horizontally below the header image. This choice shows only the first sublevels of all topmenus in different lines below eachother. See image left and below: the first line in the submenu is the sublevel of "Home" (blue arrow), the second line is the sublevel of "The Menus" (red arrow).
For second level navigation, you decide if you'd prefer it vertically in the sidebar. This choice allows for further sub-levels of navigation (see image left), or horizontally below the header image. This choice shows only the first sublevels of all topmenus in different lines below eachother. See image left and below: the first line in the submenu is the sublevel of "Home" (blue arrow), the second line is the sublevel of "The Menus" (red arrow).

