Building an app is a big project. If you want to build the next great smart phone app. You need a plan. First, think what kind of app that you want to build. Will your app be a game? Will it be for business? Then make a schedule for building the app. You need plenty of time for research before you are ready to build.
Now you are ready to make the app. Building an app is like a puzzle with many different parts. You can build it yourself or find a company to help you. There are many videos and websites that can teach you to build one. Some websites provide "building blocks (应用组件)" for app developers. As you build, you pick blocks from the website and put them in your app.
After you build your app, you need to check it carefully. Look forbugs. Most apps have several problems to fix. Show your app to people. Ask their opinions. Make sure everything works before letting people download it. There are so many tools that can help you build apps. Having the right tools will make the work easier. Now almost everyone can make a new app.