With roughly 2.1 billion people around the world now using a smartphone, the mobile app market has never been more lucrative, with Android and iOS dominating the smartphone operating systems. You will need to decide exactly which type of smartphone user you want to target first if you don’t want to build both at the same time. As they are two very different mobile platforms that require two very different types of language (Android apps are predominantly done in Java, while iOS ones are mostly done in Objective C or Swift) and native UI / UX design.
For total market penetration, you will eventually want to develop for both iOS and Android. In order to save money in the long run, you can choose to develop your app in Cross Platform although native development is more ideal for scalability and flexibility purposes.