Bottom right blue circle with icon of a road sign - right turn <↱>. It is quite useful button, it can show you also time tables for public transport near you. But I discovered it by accident so it is not that evident as most icons.

But usually if I want to search for directions not to or from current location I just search for destination and later just change current location to different thing.

What is missing for me is the ability to select time of arrival/departure for car navigation. It is useful to see how traffic is predicted to look like in advance. But you can get something a bit like this (with just enough advance) by creating event in calendar and using Google Now. It will notify you when you must go with taking traffic in consideration.