We are in the process of writing up a detailed account of VeriCoin's staking system. Here is a wikipedia on PoS generally with additional links, the system was started by PeerCoin and our system is based on theirs. https://en.wikipedia.org/wiki/Proof-of-stake
To answer your question, in VeriCoin you only need to open your wallet once a year to earn interest. However, all the time your wallet is open you are earning compound interest and transactions fees. So you will earn interest in a complete cold storage wallet opened once a year, but you will earn more by keeping it open.
Oh wow, thats cool, so its like a mini-payment for helping the network? Ill read the link.. thanks!