I use bluewallet daily.

Bluewallet supports two kinds of wallets: on-chain and custodial-lightning. Other lightning wallets support noncustodial lightning, but let's not go there for now.

In-geneal, BlueWallet isn't for HODLing multiple bitcoin because you're carrying it around with you all the time in your phone. For that you want something that supports offline wallets (like Sparrow). If you want to keep it simple, pull your sim card on an old phone, wipe it, install bluewallet and use it like a hardware wallet. Be sure to write down your keys and keep it in multiple safe places. Be advised, a multisig wallet isn't quite what you expect, you need to store a special file in addition to your key phrases.

Bluewallet on-chain wallet support is excellent. They support many important features and the interface is very good. You can also run your own electrum server and connect your bluewallet to to in order to keep your wallet addresses private.

A lightning node is built around two kinds of bitcoin wallets: a regular single-signature wallet, and several two-signature wallet with a contract called a HTLC. The two-signature wallets are also called payment channels, and this is how funds are exchanged between nodes.

Lightning on the backend is built on this idea, a shared wallet with a digital contract (HTLC) that has a "don't screw me" clause built-in. That clause needs to have enforcers on the network, and they have to know details about your private transactions in order to do so. The enforcer of your contract can be your node, or something called a watchtower. A watchtower is like having a backup-node on the internet to keep your wallet safe.

There are two ways to get funds into your lightning wallet: Either someone fills up available inbound liquidity on one of your lightning payment channels by paying your invoice, or you send on-chain funds to your node's single-signature wallet. At a later time you can assign these single-sig wallet funds to a new payment channel, but you can't move them to one of your existing payment channels without standing on your head (loop-in).

Bluewallet's lightning interface is very high-level. It does not expose these details about payment channels, on-chain wallets, or much of anything. You can do three things with it: pay or accept lightning payments, and add on-chain funds. All of the lightning backend stuff like opening and observing payment channels on your node are not accessible from bluewallet. Bluewallet is designed to keep these details hidden so all your grandma needs to know is how many sats she has in her wallet and how to scan a QR code to pay for your happy meal.

With bluewallet lightning YOU MAY be the custodian by running your own node and then create a lndhub wallet on it with your app. Alternately (and by default) the wallet will use bluewallet's managed lightning node and wallet service. Its called LNDHUB. Basically whoever's lndhub server you're using is where your lightning sats reside and its fundamentally a 100% reserve bank. You have to trust who ever is managing the lightning node, and that they won't operate at fractional reserve. They can if they want to and theres no way for you to know.

I really like bluewallet and lndhub because I run my own lightning node with my always-on server so I know where my bitcoin is at all times. Without running your own umbrel, start9 or raspibolt, you are trusting bluewallet to keep your sats safe. You may choose to do that, and that's fine, but as they say: "not your keys, not your bitcoin" so keep your funds there as low as practical.