A spreadsheet is a graphical user interface to store and organize data. It's widely used, easy to learn, and taught everywhere. Data stored in spreadsheets can be used in other applications. This process will vary depending on the technologies used. If you have a lot of data stored in spreadsheets, and you want to use this data in your application, you want to try to take the least amount of steps to get this data into your application.
The most popular ways to use spreadsheet data is with Microsoft Excel and Google Sheets. Both of these products provide APIs. The Excel API has been publicly available since Aug 3, 2016. They provide the user interface for you to create spreadsheets and share these with other users. If you don't want to be bothered with the database they use, these products provide you with the interface and an API to access your spreadsheet data.
Excel Online. With all the features users have come to expect in Excel spreadsheets, now you can share your spreadsheets in the cloud without having to pass them around in emails. Use their REST API to get a hold of your data. Requires a Microsoft account to login. https://graph.microsoft.io/en-us/docs/api-reference/v1.0/resources/excel
Google Sheets. Another alternative for Google users, part of the Google Docs family, is Google Sheets. I think they've reached feature parity a while back, with Excel spreadsheets. https://developers.google.com/sheets/
These are a couple ways to build your own spreadsheet GUI, and store data in the db of your choice or in the cloud. This gives you far more control over your implementation, and is required when you want to provide a custom user interface and create your own API to handle sharing your data between applications. The two solutions mentioned below require licenses for commercial use.
How much control do you need over the user interface? How much time will you have to implement a solution? How will you manage users and accounts? Depending on what your needs are, there are advantages and disadvantages to choosing any of these options.