I hunted around the web before I did this, but never found a tutorial showing a freeze-plug engine block heater installation on any car. (EDIT: I should say I didn't find any that I thought were more than a little bit helpful and/or pertinent.)
... probably because it isn't a common thing to do. If you live in the great cold north, your cars come new with OEM heaters, and if you don't, you presumably don't need one.
I added a heater and did it the OEM way, and wrote a tutorial.
You can read all about it here:
DIY How to Install a Block Heater, 1989 Corolla | Christofoo Review
Of course the details depend a great deal on make/model.
Let me know if you find it helpful.
Cheers,
Chris