Your data must be stored in a data management system or 'data store'. This is independent from the BRAHMS software. Currently, BRAHMS can connect to three stores, each widely used: SQLite, MSSQL Server and PostgreSQL.
SQLite is a free and portable data management system. BRAHMS uses this for RDE files and sample databases. You do not need to install anything extra - BRAHMS includes all the necessary components.
For larger databases, especially those with many simultanous users, we suggest BRAHMS projects use MSSQL Server or PostgreSQL. The express version of MSSQL Server is free but has some limitations for large databases. The full version of MSSQL Server has to be licensed. PostgreSQL is free. Both MSSQL Server and PostgreSQL can manage extremely large databases accessed simultanously by multiple users. They are 'industry standard'.
For multiple-user projects, your data store will be located on a server. Something to bear in mind is that the server has to adequately resourced. Investing in a good server with adequate store space, RAM and processing power is a key part of building a successful database project.