Yes, Lumi is an HD (or "hierarchical deterministic") wallet. That means a new, unique address is generated every time you send or receive funds, which makes your transactions harder to track, keeping your financial business yours. There’s no need to back up each address separately, all of them can always be restored using your wallet’s 12-word mnemonic phrase. All addresses generated from the same wallet can be used to receive funds, and all funds sent to any of these addresses will show up in your balance. The balance you see on your main wallet screen represents the total sum of funds in all of your added wallets (=addresses).