How do I know if my puppies are playing or fighting?

I have had, Texan, a full bred lab for a few months now and we decided to get a 2nd dog. We just got Reggie, a lab/terrier or lab/spaniel mix not sure which one....he was sheltered.....well we brought Reggie home and Texan liked him but he seems to me anyway to be jealous.....how do i know if Texan is jealous..what would he do....also Texan is only 6 months old but he is HUGE..he is 50 pounds and reggie is only 2 months and a measly 5 pounds...how do i know if Texan is being too rough? reggie seems to whine even if Texan didnt even do anything. I will say though that Reggie holds his own and nibbles on Texans ears and paws at him to protect him self.....thoughts?