Create Web App Functionality Similar to Gmail? [closed]

I’m new to web development and trying to understand how to build functionality similar to what Gmail achieves. For example, on Gmail, a user can switch from “inbox” to “sent” to “drafts” without ever refreshing the page.

Is Gmail a single page application? That seems too simple and it couldn’t handle all the functionality Gmail offers.

Any advice on what type of frameworks, functionality, design structure, etc would be much appreciated. For context, what I’ve built so far is using JavaScript and python.