This video provides a brief introduction into what a SpatiaLite database is, why you might want to use one, and how to load data and create virtual layers in QGIS 3.0. (If you are using QGIS 2.xx you’ll be able to figure it out as well)
This is one lecture of an entire course on QGIS 3.0 for GIS professionals that will be available on Udemy.com when QGIS 3.0 is released (currently expected Dec 8) so keep an eye out for it if that will interest you.
If you want to learn more, check out What can a spatial database do for you? and Quick start to spatial databases with QGIS and SpatiaLite