I was beating my head on this one, too. I have a Galaxy S6 and a 4100NEX. You will need to be sure you are using the USB2 port, as USB1 is aimed at firmware updates and for iPhone use. You'll also need to go into Smartphone setup on the head unit and set it to Other, USB2 and MirrorLink (it's in the manual). Finally on the phone you'd need to go into settinngs and look for "More Connection Settings" -> MirrorLink, but you probably won't be able to do anything there yet, just keep that screen handy.
Finally connect the USB cable to your running head unit and you should then be able to finally switch the toggle for "Connect to Vehicle via USB" and finally you'll get a connection with the unit, which will set only a mirrorlink screen on your phone and your head unit will probably say something about waiting while it reads the phone for apps or something. In any case the only app it showed for me was one called "Phone", which didn't even work. I did download Sygic Car Navigation from the Play Store, however, and apparently that is also a compatible MirrorLink app that will work with the NEX series. I'm not too sure about any other apps that might be available, however. I was REALLY hoping I could use this to run Waze, but apparently that's a no-go. You could try searching for MirrorLink (no space) on the Play Store and seeing what other apps show up that MIGHT work and MIGHT be useful to you. So far nothing is floating my boat in that department, though, so really I think the better mode to use right now is Android Auto. Not many more apps to play with there (really just Google Maps, Google Music, iHeart Radio some ability to text via voice and such) but at least it seems to work well enough. We just need a lot more apps available on it to make it more useful.
Lenny Zimmermann
Metairie, LA