Replace "theUserName" to the username relevant to your database, and "thePassword" to the password for the account you set up. Refer to the documentation of your database for details on this. Edit resin.conf and add the following under <resin>:
<database>
<jndi-name>jdbc/SKForumDS</jndi-name>
<driver type="org.gjt.mm.mysql.Driver">
<url>jdbc:mysql://localhost/forum</url>
<user>theUserName</user>
<password>thePassword</password>
</driver>
</database>
<database>
<jndi-name>jdbc/SiloDS</jndi-name>
<driver type="org.gjt.mm.mysql.Driver">
<url>jdbc:mysql://localhost/forum</url>
<user>theUserName</user>
<password>thePassword</password>
</driver>
</database>