Yes, web apps can work offline using a technology called "service workers". Service workers allow web developers to cache essential resources such as HTML, CSS, and JavaScript files, so that the web app can still load and function even if the user's internet connection is lost or intermittent.

Service workers are scripts that run in the background of a web app, intercepting network requests and returning cached responses when the network is unavailable. This allows the app to provide some basic functionality, such as showing cached content or allowing the user to interact with the app while offline.

Web apps that are designed to work offline typically use a combination of service workers and client-side storage technologies, such as IndexedDB, to store and retrieve data locally on the user's device. This allows the app to continue functioning even when there is no internet connection.

It's worth noting that not all web apps are designed to work offline, and those that are may have limited functionality when offline. Additionally, some features, such as live data or real-time updates, may not be available when the app is offline.

Web apps store and retrieve data using different techniques, depending on the complexity and requirements of the application. Here are some of the most common ways web apps store and retrieve data:

Cookies: Cookies are small text files that web apps store on a user's device. They are used to store information such as user preferences and login credentials. Cookies are primarily used for session management, and they can be accessed and modified by the web app that created them.

Local Storage: Local storage is a way of storing data on the user's device using the web browser's built-in storage mechanism. Local storage allows web apps to store larger amounts of data than cookies, and the data persists even after the user closes the web app or shuts down their device.

Session Storage: Session storage is similar to local storage, but the data is only stored for the duration of the user's session. Once the user closes the web app or logs out, the data is deleted.

Server-side Databases: For more complex web apps that require large amounts of data storage, server-side databases are used. Server-side databases such as MySQL and MongoDB store data on the server, allowing web apps to access and manipulate the data using queries and APIs.

RESTful APIs: RESTful APIs allow web apps to retrieve and manipulate data stored on the server. APIs provide a standardized way for web apps to interact with server-side databases and other web services.

Overall, the choice of data storage and retrieval technique depends on the specific requirements of the web app, such as the amount of data to be stored, the type of data, and the level of security required.

Websites are primarily designed to provide information and display content, while web apps offer more advanced functionality, such as interactivity and data manipulation. Web apps are often designed to perform a specific task or solve a particular problem.