The money lines indicate how much money you are about to win when betting on particular amount of money.
They also indicate how much money you need to bet in order to win 100 dollars. For example, if the money line indicates -120, it means you will gain 100 dollars on each 120 dollars you bet. In order to win that amount of money, your team has to win, regardless to the game final score. If the money lines indicate 120, you would gain 120 dollars on each 100 dollars you bet.
Money lines appear as minus symbol or plus. The preferred team, which is the team you believe to win, is expressed with the negative numbers. The underdog, which is the team you believe to lose, is expressed with positive numbers.
Money lines negative numbers designate the amount of money you have to bet in order to win 100 dollars and the positive numbers is the amount of money you would win if you place a bet worth 100 dollars.
The money lines have also an over and under number, which is the joint number of the score points the experts estimate the game will end. Your bet is on whether the joint score will be over or under that number. Generally, in order to win 100 dollars your bet will be around 110-120 dollars.