Your Idea. It’s not enough to say that you’re going to offer an exercise classes. The people considering your classes will want to know exactly what they are going to get for their money, and it will be up to you to explain it concisely and effectively. Understand that you’re basically giving a sales pitch to potential attendees. You’ll have to really narrow down your topic.
One thing, though, there is a big difference in making an app for Android and an app for iOS, and that is the fact that making an app for Google Play costs just 25$ one-off, making an app for iOS costs 99$ a year, so if you are making an app for iOS, I will recommend you to be a bit more confident about the way you will make money by your app, than if you are making an app for Android.
If you’re new to blogging, and want to learn how to make money at home but aren’t quite where to start, I’d consider starting a WordPress blog (like this one) with HostGator. It’s a low cost way to start your own online business (less than $5/month) and HostGator offers a 45-day money back guarantee if you deciding blogging just isn’t a good fit for you.