If you wanted someone, perhaps an employee or a public official in California, to do you a favor and you were to offer the individual something of value in exchange, that might be an act of bribery in the eyes of the law. If that were the case, then both the person offering the bribe and the person accepting it could face criminal charges.
The elements of a bribery charge can vary based on who is allegedly involved and who is prosecuting. For example, the federal government prosecutes bribery cases against elected officials and/or federal employees according to very specific elements. However, when bribery is not a federal case, the prosecutor must prove two basic elements, that the intention behind the bribery was corrupt and that the purpose of the bribe was to alter the action of one or more individuals or influence them in some way.
Although the two are easily confused, bribery is not the same thing as extortion. Extortion involves using threats of negative acts, such as violence, to get someone else to act in the way that you want. Bribery, on the other hand, involves influencing someone in a positive way to do what you want by offering them a reward for the desired behavior.
There does not need to be written evidence of bribery for a prosecutor to prove that a crime was committed. A video or audio recording, such as from a police body worn camera or a recorded phone conversation, would provide sufficient evidence that an agreement took place.