Outgoing calls

Just started to work with Jitsi. Most of the things are simple and work out of the box.

I am new to SIP and have few basic questions:

Issue

We have a platform that takes care of the meetings, schedules and other aspects of operations. When someone checks in and no resource is available to enter the meeting, we would like to call a phone number.

Question

What do I need in order to initiate the call from Jitsi to a phone number?

Thanks in advance