If you’re just bowling with your friends during open bowling time, you can really pick any rules you want. You might have everyone compete against each other for the best overall score, or you might pair up with a friend and have your combined score go up against that of another twosome. Also, if you’re just in it to have a good time, you might not even care to look at the scores.
The only time the rules really matter is if you’re joining a league. If you choose this path, there are endless variations, and your bowling center will make it very clear what rules are in place. The most common format is to have the total score of your team against a team of opponents, and each bowler receives a handicap added to their score based on their average score. This is designed to even the playing field and give everyone a fair chance at winning. A better bowler would get fewer “handicap” pins added to their score, and a beginning bowler would get more pins tacked on.
Recreational bowlers have come up with some other great rules for group bowling. A popular one is to agree that the lowest score wins and try to have bowlers hit the fewest pins. To make this work, it’s good to count a gutterball as a strike so that players can’t just throw it in the gutter and win.
You could also have each bowler use their non-dominant hand for bowling. Some bowlers like to experiment with different styles of releasing the ball, such as “granny” style. If you’re going to try anything like this, however, be sure to be safe and not upset the staff at the alley.