With the release of version 3 of QGIS comes a host of new features and tools—far too many to document here, but if you are interested, take a look at http://changelog.qgis.org/en/qgis/version/3.4-LTR. For the new addition to QGIS 3.6, have a look at this http://changelog.qgis.org/en/qgis/version/3.6.0/. The biggest shift in QGIS 3.x is the migration from Python 2 to 3, which has extended the functionality to run scripts, processes, and tasks. Further to this, the underlying application used to build the QGIS interface, called Qt as of version 3.x, runs off Qt5.
To highlight perhaps just a few of these new features, note the following:
- Data Source Manager: The Data Source Manager (accessed via  or Ctrl + L) is perhaps the most notable visual change of 3.4, as it is presented as the default tool to accessing data to load onto the Map...