A 1st Q moneyline bet allows a bettor to wager on which team will win the 1st quarter without having to deal with a point spread. A win by any amount will cash the bet regardless of what the spread was.
Instead of a spread there are odds associated with each team to balance out the bet. If you are betting the favorite you will have to lay additional money while an underdog gets a additional winnings if they win outright.
Lakers -115 vs Mavericks +105. In this example the Lakers are -115 to win the 1st Quarter while the Mavericks are +105. You would have to bet $115 to win 100 if you bet the Lakers while for the Mavericks you would win $105 off a $100 bet. The easy way to think about moneylines is the "-" is how much you need to bet to win $100 , while the "+" is how much you win off a $100 bet.