How to start ION Integration with third-party software from the beginning?

Hi,

I have been working on LN(10.5), ION, and an in-house software of the company I'm working with for some time. Now there's an idea to integrate the in-house software to connect with LN via ION.
So, the question is how to do the integration part of a third-party software (the in-house software) into ION and then connects to other products such as LN in this case.
Where should I start?
What are the prerequisites?

Regards,
Thana