Once you have done system installation you can do base system config and install some useful tools to use it as server for example on VM as local environment for web development.
The root user is the administrative user in a Linux environment that has very broad privileges. Because of the heightened privileges of the root account, you are discouraged from using it on a regular basis. This is because part of the power inherent with the root account is the ability to make very destructive changes, even by accident. Base step is to set up an alternative user account with a reduced scope of influence for day-to-day work. After installing Debian by default you should have one alternative user and you can skip this part but if you want to add new one use following command in terminal once you are logged in as root:
adduser bart
- where bart is a name of new use