Low level contracts in bridge are called part-scores and the bonus for making a part-score is 50 points. A game in bridge is a contract of 3NT, 4♥, 4♠, 5♣, 5♦ or higher. The bonus for making a game is 300 points if you're not vulnerable and 500 points if you're vulnerable. If you think might be strong enough to make a game it's often worth giving it a shot but how can you tell?
If you and your partner have 25 points between your two hands then you'll have a fair chance of making game.
Keep in mind that 25 points doesn't guarantee you'll make your game but the bonus points for making game make it worth taking the risk.
If you do have enough points to bid game then 3NT will often be your best contract because you only need to win 9 tricks.
North opened the bidding showing 12 points, South has 13. That's 25!
Hearts and spades are called the major suits. If your bidding tells you that you and your partner have 8 hearts or 8 spades between your two hands then 4♥ or 4♠ is probably the way to go. 8 cards in a suit is called a 'fit'. You'll need to win 10 tricks to make 4♥ or 4♠ but the trump fit will often be worth an extra trick or two.
North and South have a trump fit.
Clubs and diamonds are called the minor suits. 5♣ and 5♦ need 11 tricks.
Hmmm, might be better to try 3NT.
When you and your partner are bidding you want to try to get into a situation when one of you knows whether or not you have enough points for game. For example, if I know you have 12 points then I can add my points to what you've shown and calculate the total. So you'll use some bids to search for the right suit to play in. Then one player will make a bid to show a specific strength and shape and that will allow that player's partner to decide how high to bid.
So it can be helpful to think of every bid as falling into one of three categories.
When you're bidding a new suit keep the bidding as low as possible to give your side room to explore.
South bids 1♥, keeping the bidding low.
When you're making a limit bid you bid as high as you can You don't need to save bidding space now because you're pretty sure you know if you're going to play in a suit contract or notrumps. Now's the time to describe your strength.
South has found a spade fit. 3♠ is a limit bid.
After one player has made a limit bid to show their points and shape that persons partner will be in a good position to choose the final contract.
North has something extra and bids game.