Just buy small amounts of bitcoin. 1 sat = 1 satoshi = 0.00000001 BTC = less than a penny right now.
Of course people don't stack individual sats at such a price, they just buy as much as they can afford, as much as they feel comfortable with buying and make sure it is somewhere they think is safe.
If you are collecting your sats in an exchange, this is okay but once it is more than you might carry in your pocket, move it to a bitcoin wallet that you have full control over. Coinbase wallet, Binance wallet, Exchange XYZ wallet, these are not bitcoin wallets, BlueWallet, Sparrow Wallet, Phoenix Wallet, Samurai Wallet, these are Bitcoin wallets.
Do spend some time looking up the differences between the wallets, do ensure you are keeping "open source" and "self custodial" as the most important features before things you might want like "lightning payments", "coin joins", or "multiple accounts" etc.
You won't get a lightning address from a custodial wallet other than nostr:npub1xnf02f60r9v0e5kty33a404dm79zr7z2eepyrk5gsq3m7pwvsz2sazlpr5 as far as I know, but do shop around, do experiment and find the best one for you.
Anyway, the stacking part is easy. I hope you got it.