it's just a way of making multiple parlays. so if I pick 5 fights, I can put them all in 2 way or 3 way round robin. that puts every possible combination of my picks in a 2 or 3 pick parlay.
So if my picks are: A, B, C, D, E
a 2 way round robin would make these parlays: AB, AC, AD, AE, BC, BD, BE, CD, CE, DE.
a 3 way would make: ABC, ABD, ABE, ACD, ACE, ADE, BCD, BDE, CDE (you get the idea, not sure if I got all the possibilities)
it increases your odds of hitting on a parlay since smaller parlays are more likely to hit than big parlays. It requires you to make more bets obviously, but your potential winnings are much greater than if you bet each fight individually (unless you bet big on just one underdog which I wouldn't recommend).
the bovada website makes it really easy to do just from your smart phone. im not familiar with teasers. ive done a couple prop bets (x wins by decision, x wins by stoppage) but rarely.