I wonder principle mixer vst

do you know send vst and mixer vst 

one day i watch this video



so they use vst plugin, but there are 3 types, one is send plugin, the other is mix plugin, last one is out plugin


so i try to make mixer track( empty track, like aux receive) and connect my test vst plugin. and i get only mixed sample data.(not seprate sample)

i can't get multiple sample.

so i think another point. is this use inter process communication, just send to sample data using vst plugin.  process in mix plugin, and send out plugin?