A wallet stores the information necessary to transactions YEScoin's. While wallets are often described as a place to hold or store YEScoin's, due to the nature of the system, YEScoin's are inseparable from the blockchain transaction ledger. A better way to describe a wallet is something that "stores the digital credentials for your YEScoin holdings" and allows you to access (and spend) them. YEScoin uses public-key cryptography, in which two cryptographic keys, one public and one private, are generated. At its most basic, a wallet is a collection of these keys.
There are several types of wallets. Software wallets connect to the network and allow spending YEScoin's addition to holding the credentials that prove ownership. Software wallets can be split further in two categories: full clients and thin clients.
Full clients verify transactions directly on a local copy of the blockchain, or a subset of the blockchain. Because of its size / complexity, the entire blockchain is not suitable for all computing devices. Thin mode on the other hand consult a full client to send and receive transactions without requiring a local copy of the entire blockchain. This makes lightweight clients much faster to setup and allows them to be used on low-power, low-bandwidth devices such as smartphones. When using a lightweight wallet however, the user must trust the server to a certain degree.
Coin age based selection YEScoin's proof-of-stake system combines randomization with the concept of "coin age," a number derived from the product of the number of coins times the number of days the coins have been held. Coins that have been unspent for at least 30 days begin competing for the next block. Older and larger sets of coins have a greater probability of signing the next block. This process secures the network and gradually produces new coins over time without consuming significant computational power. YEScoin's developer claims that this makes a malicious attack on the network more difficult due to the lack of a need for centralized mining pools and the fact that purchasing more than half of the coins is likely more costly than acquiring 51% of proof-of-work hashing power.