Dbcalls in Camunda?

Hey,I am having a hard time connecting camunda to External DB. I know we need to use java class To connect, I am trying to connect Oracle Database,
so if somebody gives me some brief idea about how to connect it to DB I’ll be highly greatfull.

Do you any application server to run Camunda ?
Then look
https://docs.camunda.org/manual/latest/installation/full/
for information.

Parent topic is
https://docs.camunda.org/manual/latest/installation/

I am using Tomcat Version of camunda