TYPO3 CMS relies on storing its data in a Relational database management system (RDBMS). The Doctrine dbal component is used to enable connecting to different database management systems. Most used is still MySQL, but thanks to Doctrine others like MariaDB, Postgres, Oracle and SQLServer are also an option.
During the install progress you can select the corresponding DBMS.
At the time of writing the installation process does not fully work for SQL Server, the connection settings have to be manually configured in that case.