We really don't know.
It's likely that demonic looking creature is some servant of Darkseid, but we don't know for sure.
It could be Yuga Khan (Darkseid's father), or Steppenwolf (a genral in Darkseid's army). Both wear long horned helmets, but neither really look like the creature we see in that scene. But whatever tech is being used seems to be only displaying an approximation of whoever Lex is talking to, so they probably look very different at the other end of that communication.
Those boxes are very likely Mother boxes, like the one we see in the Cyborg scene earlier in the movie. They are crazy advanced New Gods tech used for all sort of things. But, if that creature is a servant of Darkseid, those boxes could be Father boxes, which are Darkseid's version of the Mother box.
Why Lex is attempting to communicate with the creature is a mystery. He could be promising earth to Darkseid in exchange for power of protection? We don't know yet.
Ankit Sharma's answer over on the Movie Exchange is (some might say) superior to mine :)
Worth a look:
Who was the horned creature luthor was seen with in Batman V Superman: Ultimate Edition?