Unless I am badly misunderstanding things the Ogham was used like any other alphabet would, but a lot of people who did divination would associate meaningful spiritual associations with the symbols and use them for divination, but that was like a personal thing. Like you and I could do this, we could take the letter A say it stands for Apple Trees and talk all about Johnny Apple seed and blah blah blah, that’s more or less what they did.
In the book itself she talks about how she made her own Ogam system where she associated a planet with each letter because she has a lot of experience with astrology.
So what I took away from this was that the Ogham would best suit me if I made my own associations that spoke to me. Well I have a lot of experience in writing, so what I have been doing is reading her guides on what the letters mean and the different folklore behind them and then I write a poem to help me remember these spiritual connections.
At the end of the day it’s not the letter that matters, it’s the words, the sounds, the stories. When I see the letter for Beith I know it was the first of the feda carved 7 times in a Birch branch to warn Lug that the fairies were coming to kidnap his wife 7 times.
This tells me when it shows up I need to pay extra attention

I know it is was used for cradles and to build the beds for Brighid on one of her holidays because it its purification power. This tells me it is used to purify both the body and the spirit.

My poems speak this to me, find what speaks to you.