To "Cast" from an andriod go to the play store and search for ES File Explorer.. I think you also need a chromecast add on.
It is requirted that your 'droid and dongle both be connected to the same router as I recall less the droid is in Ad-Hoc (Wi-Fi Direct) mode.
NOTE Not all video files will cast.. I have a ton of MP2 files these are Video and in fact I am watching one recorded last night as It type. (Columbo)..It will not cast w/o conversion..
MP4 generally works.. I have not tried other formats. (I am sure several will but I have not tried them).
Again that is ES-FIle explorer, ES-File player and if needed the chrome cast add on.. I do know it works great from my 'Droid.