Your RVN Wallet connects directly to the Ravencoin network. This improves security and privacy, but also means sometimes your wallet can get out of sync with the network. Syncing with the blockchain can take a lot of time, and usually isn't necessary. If someone sent you Ravencoin and the transaction is confirmed on the blockchain, but it is not appearing in your wallet, your wallet may be out of sync. First check to make sure the address the Ravencoin was sent to is correct. If you are trying to send Ravencoin and constantly get an error message that your transaction was rejected, it could also mean your wallet is out of sync. In either of these cases, using this feature will rescan the blockchain to find your Ravencoins and display it properly in your wallet. Visit this page for instructions on how to sync your wallet to the blockchain.