This, definitely this!! For the most part, it isn't hard, just very different from the scanners of old... It's entirely database-based, with a master database and smaller databases that you make or import, called "favorites lists". Sure, you can directly enter frequencies, and save them in a favorites list, but it's not like a memory entry in a bank. And everything you need to know about what to do is available in the manuals we've linked, or you can search for answers here (and ask, if you're unable to find anything yet).
Additionally, you can use (import) anyone else's favourites lists, made for any of the SDS and HP series of scanners (any of the scanners that use either version of Sentinel), that you can find here or elsewhere.
Nextly, you can decide to buy upgrade keys for DMR and NXDN (as well as ProVoice, which isn't used much, and the Waterfall function, which isn't strictly necessary, but can be useful), to greatly expand what you can scan for on your SDS unit.
And lastly, I'll repeat myself, and again say DON'T PANIC!! You don't need to know everything all at once! I've had mine for over a year, and I'm still learning (and I have no regrets)..... 🙃