Hello
Apart from the LibreOffice Base handbook, you may find these video tutorials to be of use:
https://thefrugalcomputerguy.com/seriespg.php?ser=15
I hope this helps you if you are just getting started. 
LibreOffice Base - migration from HSQLDB to Firebird DB
Hello
LibreOffice Base can work with either an embedded database, as a “stand alone” database, or as the front end for a variety of server-based databases such as “MySQL” or “PostgreSQL”.
The Document Foundation has a project which is nearing completion, to replace the embedded HSQLDB database with an embedded Firebird database. See:
In the actual stable version of LibreOffice 6.0.7 (my Ubuntu-Mate 18.04 installation has version 6.0.6.2) you are supposed to be able to “try out” the new Base-with-integrated-Firebird database. See:
https://wiki.documentfoundation.org/Development/Base/FirebirdSQL#How_to_test
The “graphical way” did not work for me, I could not establish a connection to the database, the error message pointed to a failed “firebird sdbc connection”.
I have not been able find a solution on the internet. However, I do have a “work-around”.
I spun up a Virtualbox VM for Ubuntu-Mate 18.10. Then I installed the latest testing version of LibreOffice (i.e. 6.2.0 RC1) from “https://www.libreoffice.org/download/pre-releases/” (lots of individual debs to install - in the correct sequence of course!). In version 6.2.0 Firebird becomes the default embedded database. Here I was able to create a new “embedded database” without any problems.
I now have a “testing” environment and will explore the functionality, step by step.
I hope some of you may find this information to be of use.