To develop an app like Instagram, you need to understand the objective of your app. Instagram allows photo-sharing, direct messaging, and selling products. So, decide what's your purpose. Based on it, the features and tech-stack would vary.
If you want to build a custom app, you would need extensive knowledge of front-end and back-end features, APIs, etc. Well, you can skip and go for clone apps, but that won't be flexible if you're starting a new business. A development team can help you guide with the right set of knowledge and expertise to build an Instagram-like app.