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First-Person Shooters (FPS) are games where multiple players join opposing teams and shoot each other. You will often win by either eliminating the opposite team, exploding a bomb, or running out the timer.
Good communication between players is often essential in winning. Serious players will have voice communication, but its also good to have in-game comms to easily communicate tactics. In coherence there is the concept of Client Connections which you can use to easily send messages between players. It can also be used to communicate game state changes e.g., "The bomb has been planted".
When building your level there may be certain objects that should be duplicated across Clients. You want to have a duplicate of each player on every Client, but for something like doors which can be opened or closed, you only want one "shared" door across all Clients. For this to happen you need to understand Uniqueness and Lifetime. Using those concepts, you can make sure that a given objects is persistent on the scene, and that only one exists.
Similar to doors, the bomb is also unique. The difference is that the bomb is spawned and only 1 bomb can exist in the game at any time. Doors are also unique, but multiple instances of a door asset can exist, just not at the same place. To understand more, read about Setting up a global counter. This is the same principle of having a Prefab that is uniquely identified.
Online competitive multiplayer games are tricky to get exactly right, and there is no "right" solution. It's a constant tradeoff between cheat protection, latency, client prediction, etc. You need to do further research to decide on the solution that best suits you. One thing you definitely need to learn about is client vs server authority.