You have to decide on what kind of app you want to create. Let us give you more insights into the different kinds of apps that are relevant.
• Web App: A web app is a specific layout for a phone or tablet’s browser which is more user-friendly and optimized then regular website. With apps becoming more and more popular a lot of ideas get developed without consideration if this idea can become an end-product with developing “only” a website that has a “mobile version”.
• Native Apps: A Native App is a stand-alone, downloadable app that is specifically available for either iOS or Android and what you develop for one will not translate to the other. For that reason, you’ll find plenty of platform-specific apps that live on one or the other, but not both. This can be relevant if you have time and budget to create two apps (if you do not want to decide on either App Stores) or your app idea fits only one mobile app store.
• Hybrid App: A hybrid app is one that kind of gives you the best of both worlds. You won’t get all of the creative control that you get in a native app, nor the flexibility found in web apps, but you end up with a good mix of both without having to spend the same amount of money and time.