how to get Xenochips?

I am not an English speaker. But I have a question. How do I get Xenochips?
What mission? What quest? Or what?

In Wiki, Portal battles and Alien boss battles. It is said.
But “Alien boss battles.” I don’t understand. What is this?


Please explain easily.

All missions should give them. You can see a small xenochip icon on the missions that apply to the event.