Here you can create a new wallet, copy the wallet definition to a local file or set the wallet definition from contents you saved previously. To setup your web wallet, you give it a name and press the New button. The wallet only lives in memory, so you should consider exporting it if you want to save it between sessions. The name is just for your reference, so you can tell different wallets apart, and the id is generated and is an internal id of the wallet in memory.
For test purposes, a wallet will only exist 600 seconds inmemory cache. After time is up, you need to either set it again or create a new wallet.