I will use tonight's Patriots Dolphins game to help explain.

Over/Under: This is the total number of points scored in the game. Tonight's over/under is 51.5. If you think tonight's game will be a shootout with a lot of points scored (i.e. final score 31-28) you should bet the over. If you think tonight's game will be a defensive struggle (i.e. final score of 24-20) you should bet the under.

Spread: This number is determined to make a fair playing field for people betting on both teams. Tonight's spread is Patriots -8. That means the patriots are favored by 8 points. If you want to bet on the Patriots giving 8 points then they would have to win by 9 or more points to win the bet. If you bet the Dolphins getting 8 points They would have to lose by 7 or less points, or win the game outright for you to win the bet. a score of 28-20 would be a push meaning no team wins and you would receive your money back.

Money Line: This is a bit more confusing, but this is used if you want to pick a team to win with no spread. (i.e. if you are confident the patriots will win, but not by 9 or more points). But since the patriots are the better team and at home you would need to risk more money. The money line for tonight's game is Patriots -430 and Dolphins +315. -430 means you would have to risk $430 if you want to win $100. +315 means $100 bet would pay $315.

These numbers will change depending on which team or over/under is being bet on more. The bookies and vegas make money by having the same amount of money wagered on both sides. When you lose a bet you have to pay the juice. Which is generally $10 for $100 bet. If you bet $100 on the Dolphin +8 tonight and they lose by 9 you would owe $110.