In Media Encoder with the file highlighted click on the Format or Preset link [left end of line - burnt orange color by default]
Either will bring up the Export dialog
From there you will have a long list
If you click Preset you will get a VERY long list of devices to choose from. Just make sure the preset matches your input and/or your desired output resolution and frame-rate/
http://blogs.adobe.com/kevinmonahan/2012/04/23/exporting-media-using-a dobe-media-encoder/
Ih Lightroom, if one of the three choices is not to my liking
I export to a sub folder and then go to Media Encoder.
