If it is not done yet, download the latest release from apache tomcat website.
Uncompress the archive inside a folder of your choice.
Using a text editor, open the file context.xml in conf/ folder.
Add a jdbc connection to your database. It sould look like this:
<Resource name="jdbc/aegaeon" auth="Container" type="javax.sql.DataSource" factory="org.apache.tomcat.jdbc.pool.DataSourceFactory" username="aegaeon_server" password="password" driverClassName="com.mysql.cj.jdbc.Driver" url="jdbc:mysql://localhost:3306/aegaeon_db"/>
The resource above use MySQL driver. If you are using PostgreSQL, you will need to use a different driver. This is a very minimal jdbc connection setup. I highly recommend to check tomcat's connection pool documentation to setup the maximum number of connections and other important properties of your database connection.