GeoJSON is becoming a common data storage format for sharing data, especially in the open source world. GeoJSON is very convenient for web GIS applications and for smaller amounts of data, a zipped GeoJSON text file is often the most compact option as it lacks the overhead of some other storage formats. You can learn more about the details of GeoJSON, and why you might want to use it here.
The video below provides instruction on how to save a shapefile as a GeoJSON text file in QGIS. If you want to learn more about creating your own web maps, please check out my courses on Udemy.com.