Hi, welcome to Bubble!!
Let’s start with understanding what you mean by “mobile”. Do you mean native or mobile-first web design (i.e.: browser mobile).
Browser
You can visit both Groupon and Yelp (and indeed almost every app worth it’s salt that is not a game) on your mobile device, without having installed an app. You use a browser such as Chrome, Safari, FFox, Opera, etc. to access an website. Bubble excels at this, because you get cross-browser support out of the box, a pretty intuitive responsive builder and the way the rendering engine works is that it only paints the parts of bubble site it needs to display for it to function, making it a really low-maintenance architecture with little bloating and very good support. The web isn’t the wild west it used to be and having a team of experts constantly keeping your site up to date with things like accessibility and seo without needing to know how to code is really worth the price tag. Add the ability to display dynamic content and create a customized user experience, you have yourself a winner. I’m beginning to see UX designers adding the line “no app required” or “no download needed” across the web, so it seems starting with this may be a good way to build up your user base.
Native apps
This is what you find on Google Play and the App Store. These apps are installed to a device and connect with a database to display content. There is currently no way that I’m aware of to create a native app in bubble. I understand it is on the roadmap, but I’m not familiar with the specifics so I’ll let someone else chime in here.
Hybrid apps
Over the last few years, we are beginning to see apps built for browsers being “wrapped” and submitted to the App Store and GPlay. This means that the “native app” itself is actually a service that displays what you’ve built for web when the user opens the app on their device. I suppose it is faster to add/remove/modify things this way because you don’t need to do it three times (once for web, and once for each platform). From what I understand, you change everything once and it applies across platforms. You can indeed use Bubble this way, there are a few success stories on the forum and reaching out to those developers may give you a bit more context. I’ve just begun experimenting in this domain. The point is, when you’ve created something that your users enjoy, you do have the ability to move it to a native platform.
Using Bubble as a backend
What you’re referring to when using bubble as a backend is setting up your data architecture on bubble and exposing and API, then “hand coding” your native application and using your native app to interact with the Bubble API you’ve created. It is neither the quickest or cheapest way to set up your own backend that I’ve encountered. I’ll let people with more experience in data architecture chime in here as well, but something I won’t do is recommend alternative platforms on the Bubble forum.
Unsolicited advice
I don’t want you to be mislead and think that you can sit here and build Groupon overnight. But I do want you to believe you can sit here and build Groupon using Bubble. Using this platform has it’s limitations, but also it’s strengths. To me, it’s the next logical evolution of programming, making app-building accessible to people who don’t have five years or $20k+ to spend on a wireframe.
If you’re a visual learner and you know little or nothing about data architecture, design, development or app building Bubble is a great way to learn because of how quickly you can test and iterate different things in a visual way. I would compare it to learning what shapes are using this game vs learning what they look like using mathematical equations.
Similar result, much easier to do visually.
Finally, this community is amazing. You can learn so much on this forum it’s insane. I wish you good luck on your journey, and if you’re sticking around, we’ll be happy to see your progress 
