I never have a use for one, but I am aware that many people like to use libraries such as ShapecastHitbox for collision detection.
Use UserInputService to detect user input.
Alternatively, if you’re using a Tool instance there is also a Tool.Activated script signal.
It is best to keep things that are visually rendered on the client, such as animations and particle effects. The server should be used to inform other clients that they need to perform these effects on their own client. Additionally, the server should be used to perform any authoritative actions, such as applying damage or validating a damage input request from a player.