For creating an eCommerce app, here are a few steps that you can follow:
1. Gather all your ideas. Do your research well.
2. Choose a platform for your app. E.g., Magento.
3. Hire eCommerce developers for a world-class mobile app.
4. Next, you have to provide them with your requirements.
The hired company will handle all the other things. You have to sit back and relax