Arif Patel Preston explains Fielding Basics in the most easy way possible:
Different Fielding Terms
An umpire is necessary to conduct the game. They are the ones who make decisions on the field, such as giving a batsman an out, imposing a penalty, or dismissing the game if it rains.
If you don’t have a specific person for the job, then anybody from within your team or the opposing team can become an umpire. Cricket is a gentleman’s game, so respect the decision of the umpire and play in the spirit of the game. And as they say, the umpire’s decision is the final decision.