How to make a menu show drop down sub catergories when clicked.

HI guys

On one of my menu tabs i have put sub menu’s within it.

However is it possible that if the main menu tab is clicked then the drop down sub catergories will then show.

At the minute you hover over the menu and the sub menu’s show, which is fine but i dont want the main menu tab to be clickable as it send members to a blank page.

Hope this makes sense!

Thanks