First of all you need a running database server. M4 Back Office works with MySQL, Microsoft SQL Server and ORACLE Database. It's your choice which one to use. It is also possible to use various databases of different manufacturers in one M4 Back Office. This can be useful, if you have to or want to use existing servers of different types. If you already have one of these servers running, you can use it for your M4 Back Office. Otherwise you need to setup one.
The database manufacturers provide all information you need to do so. Also they provide free versions of their products, called Community Version (MySQL) or Express Version (Microsoft and Oracle). These versions can be used for testing and also for productive systems.
Below you find useful links to documentation and downloads for the different free versions of databases and administration tools. Of course you can also use the paid versions. Also it is your choice which tools you want to use for database administration.
MySQL
MySQL is known as a database solution, popular among small and medium-sized companies. Nevertheless it is also used by industry leading companies including Facebook, Google and Adobe. Setup and administration of MySQL databases is rather simple. It is definitely a good choice, if you are not too familiar with databases. For administration you can use a wide variety of different tools. MySQL Workbench is a free database administration tool published by MySQL.
Microsoft SQL Server
Microsoft SQL Server is considered to be more advanced than MySQL. But this comes along with a slightly more difficult administration and therefore a higher possibility to do something wrong. A big advantage is its unbeatable Windows and MS Office integration. As MySQL, Microsoft offers a free community version of its SQL Server to start and maybe to stay with. SQL Server Management Studio is a free database administration tool, published by Microsoft.
ORACLE Database
Oracle is a pioneer in database technology since 1977. Its databases are regarded to be the best or at least one of the best on the market. Nevertheless it also offers a free "Express Edition". The Express Edition contains more or less all options that are available in the Enterprise Edition. Limitations are 2 GB of memory, 12GB of storage, 2 CPU and 3 pluggable databases. With Oracle SQL Developer is a free administration tool available as well.