You obtain these by completing other people's Chronicle Quests. The number of tokens awarded varies from Quest to Quest, and is dependent on the difficulty and the number of the tasks involved. As well as the the Silver Tokens that a player receives, the Chronicler receives some as well - they receive a tenth of the number that the player receives.
1000 Silver tokens can be traded for 1 Gold token.
Tokens are used to buy all sorts of rewards in the Chronicles Vendor on Coronet and Theed Chronicle tents.
You can loot 4 Silver coins per 1 Mission low level 1-2 quests. You can Loot 8 Silver coins with 2 missions on level 1-2 quests. You can loot 12 silver coins with 3 missions or more on level 1-2 quests.
You can take with you up to 4 identical quests to loot up to 48 coins per go in the above system.