How does it know IP addresses

This is probably a very stupid question but...
How does HikConnect know the IP address of a camera? If it is because the camera connects to Hik servers and therefore we have the source address then the next question is how do we know the address of the video recorder if the IP address of the home router is dynamic?

All of the explanation I have read so far make no sense or gloss over the hard bits. Perhaps it is me?