It sounds like Erin has a digital tuning box. It might also have a nicer user interface than simply tuning from one channel to another on the digital tuner in your HDTV. But if you have a modern HDTV it most likely has a built-in tuner, and all you'll need beyond that, is an antenna.
As droog said, the picture quality over the air is better than what you're going to get via cable, or satellite, or internet-based options like Hulu or YouTubeTV or Sling, simply because OTA delivery is not compressed, while the cable/satellitei/nternet carriers have to compress the signal due to bandwidth limitations.
But again, to receive OTA local HD, all you need is an antenna, provided your TV is modern enough to have a built-in digital tuner. The one I bight 13 years ago did not, the one I bought 10 years ago does, and so do all newer ones I've purchased subsequently.
And although manufacturers claim that one antenna might be better "tuned" for digital than an analog antenna, I haven't seen a lot of credible research that says this is true. There's no difference between a "digital" antenna and an older "analog" one, because there's no difference in the waves they are picking up at your house. A higher quality powered antenna is going to work better than a passive one, and the large aerials work really well. It's not uncommon to see people mounting these back on their houses these days, as they attempt to "cut the cord." Larger antennae can collect more energy and therefore capture weaker signals from further away. The shape also matters, one shape works better for VHF, another works better for UHF, and still others for the types of waves used to broadcast AM and FM radio. Most antennae from the 60s and 70s had a couple of different arrays on them, to capture both VHF and UHF signals as well as possible.
The last time I did a quick scan with my oldest digital-tuning HDTV through a small powered antenna only, in Austin, (it's the TV I keep in my RV), I found something like 40 digital channels. This is possible because a local ABC affiliate (KVUE channel 24 UHF here in Austin) actually has more bandwidth than their original signal ever used. So they're able to broadcast multiple channels across the same frequency. So I get a channel 24.1, 24.2, 24.3, and 24.4. Often one of them will be broadcast in Spanish. And maybe another one only plays old TV shows from the 60s. One of them might be an all-day weather or news channel. Likely only the main channel will be in HD, but they are all digital.
If you've never done it, you should hook up an antenna to your modern digital HDTV and see what channels you can get. If you're in a pretty large urban area, there are likely dozens. Out in the country, you'll have fewer options, but that was always the case and is nothing new.