This is a 3-day event which has a kill event that takes place on the second and third day. When you participate in a Silver War Event you will initially be given 100,000 silver which cannot be spent until the event is over. On the next two days you will be given an additional 100,000 silver so you have a total of 300,000 Silver for the event.
During day two a kill event will take place within the silver war where players will be looking to kill other players for their silver by teleporting close to their location and attacking them. Once the 3 day event has ended the silver that you have can be spent on rewards at the silver store. The rewards can be particularly useful for training/healing troops, upgrading buildings, researching, etc.
Remember that the more silver you obtain, the more appealing you become for others to attack so make sure you protoect yourself by having aegis (shields/bubbles) to protect your silver.