Creating a Tulpa
Every moment your consciousness comes and goes. Why aren't you a different person every second? Your body, your knowledge is the same. It keeps your consciousness from turning into a very different person. Thus, you are not only a flicking light but also a sum of all your experiences since birth.
Pretty much like any tulpa.
Your consciousness keeps emerging and fading; you have all kinds of random thoughts. Now, some random thought wants to stay in the head. You imagine someone. A boy, a girl you like, a horse if you're into pony fandom, a cute kitten, a huge robot. That thought wants to live on, and it turns into a tiny consciousness of its own. Just like a human body starts from a few cells, a consciousness starts from a single thought.
Bam. That thought is gone as you focus on something else. That consciousness blinked into existence and disappeared immediately. It has no experiences to stay in the body, and it can't hold to anything, the brain wipes it. Just like it wipes you and goes to daydreaming. You come back, that new consciousness is gone forever.
This book explains the practices devoted to conscious rooting of such a thought. To train the brain to keep another thought for long enough until it accumulates a critical mass of experience and can live on without external help.
There are various terms that name experiences similar to tulpas: "Headmates", "tulpa forcing", "accidental tulpas", "soul bounds", random walk-ins, book characters coming to live in your head, etc.
It doesn't matter what caused a thought to get established in your brain. All those kinds of thought forms are same --- they are consciousnesses, getting forgotten and created every moment by the busy mind. There is no difference if conscious effort creates one by reading a book and sympathizing with the character or by writing a novel.
When you actively think about a tulpa you're going to create, you keep that consciousness created from a single thought afloat. The longer the mind allows it to be aware, the more experience it gets. Eventually, it disappears as you lose the focus. Is it more than a single thought now? Maybe it got a chance to accumulate some experiences? Next time you think about the tulpa, you try to pull in that exact thought in, and the mind does that by creating a consciousness, now with some basic experiences. At some point in time, a tulpa will not require host's intervention to come up to its senses; it will become self-sufficient.