How to create dropdown menus in Joomla 3.7
How to create dropdown menus using Joomla 3. NOTE: For Protostar template, here are the extra steps required to make it work: http://codesteps.com/2013/04/29/how-to-display-pull-down-menus-in-protostar-template-in-joomla-3-x/
Also note that this method will not solve problems you are facing with templates that do not support dropdowns menus in the first place.