I think the “first step” to understand is that the Father has always existed without any deficiency. This would also include his knowledge and the knowledge of Himself and his love. The Father never had to grow up, mature, etc. He simply IS.
In the book “Theology for Beginners” by Frank Sheed, he describes it this way.
The Father is the thinker, and the Son is the thought or the Word. The thought is generated by the thinker, but the thought is separate from the thinker. There was never a time that the Father was not generating the Son, because there was never a time that the Father did not know himself, or that his thought was not a reality.
In like manner, knowing Himself to be love, there was never a time that the Father or the Son did not love, which is the Holy Spirit.
It’s not something that happens in time, rather it is simultaneous with God who exists in infinity without time. Just by his existence God can’t help but know and love. It’s not something that he has to “grow into” with time.
You could say the Father generates (not creates) the Son by knowledge, and the Holy Spirit proceeds from both the Father and Son by way of Love.
I’m doing a terrible job describing this so you might want to get the book to get a more comprehensive explanation, but I hope this helps in some way.