How to test for vaccums with smoke machine

[francesconyc]

I just got an automotive smoke machine and I was reading this article
https://www.pelicanparts.com/techarticles/Porsche_911/07-ENGINE-Smoke_Pro_Vacuum_Leak_Test/07-ENGINE-Smoke_Pro_Vacuum_Leak_Test.htm

but is not super clear where to inject the smoke.
I also saw some videos on YT and they seem way too complicated compared to his Pelican article.

so how and what to test the easy way, at least as an initial test?