I do not think you will find a single answer to that. There are many traditions, and the Italian and French Marseille practices date back to the 1400s. There are also many ways to read. Some people use astrology, psychic powers, guides, or energies along with tarot. Jungians take a psychological stance. Others use a therapeutic approach, and still others use a creative storytelling method. These are just a few of the many options.
Dad was right in the end. You shouldn't lean on the book while reading. That doesn't mean you don't read the book, though. I believe that you should know the book and also be able to read without it. It's like having a stream nearby that you can use while you listen to what other people say.
Picture a talk going on between the seeker, you, and the cards. That's the best way I can think of to explain it. The cards don't talk on their own, so you have to give them a voice. The seeker must say or ask something for the cards to say something. That could go a thousand different ways. So the better you know the book(s), the more likely it is that the "cards" (that is, YOU) will have something useful to say about the seeker's problem.
I read from the French Tarot de Marseille deck. I'm not good at reading RWS decks. But for me, the pictures on my deck are vague enough that I can arrange many of them in a way that looks like a comic strip. Lines, colors, geometric shapes, pictures or icons, structures that are the same or very similar, and lines that run through several cards. For me, these things become very revealing in their meaning. When I look at it this way, the way the cards interact with each other makes me think of new questions and pushes me to either improve an idea or come up with a new one.
When you look at a spread, try to make it a habit to imagine that the cards are talking to each other. Place your mind in the gaps between the cards to hear that conversation and bring the seeker's question, worry, or dilemma to the conversation at the same time. When you read books, you add to the pool of knowledge that you can use to find solutions. When that happens, my gut comes to life and has its own thoughts.
I've said many times that pictures don't "mean" anything until someone asks a question, shuffles the deck, and draws a card. Having said that, I've also found it very helpful to look at The Tarot in a philosophical way. How does The Fool meet the needs of freedom and stability at the same time? Or keep the fool and the wise seeker in check? How does the Magician show both the false sense of control and the willingness to let things happen as they may? How does the Papesse keep faith and doubt in check? How does she show both the holy and the common?
It is very different from understanding a card from remembering what it "means." Let me say that I think of L'Hermite as a wise [probably old] person who shuts themselves off from the world to find answers, seek the truth, and practice reflection. THAT'S GREAT! Truth, silence, seeking, and austerity are what I get. That's why I "know" what The Hermit means. That works your mind. But what do I know about it?
The monk has a lamp. Why? Since it's dark? Because there's a light? This means that The Hermit is a representation of both the darkness of not knowing and the light of knowing. Doesn't The Hermite find a balance between wanting to know things and being okay with not knowing them? The Magician , who is at the start of the number series, is a magician. Now The Hermit [VIIII] lets go of dreams and embraces reality! As The Hermit looks for the truth, doesn't he show both the knowledge of old age and the innocence of a child's mind (The Fool)? A lot of things are possible when you UNDERSTAND a card and KNOW that personality trait.
That's up to people who know more about what the RWS system can do than me.
Be careful!
Don't worry; it's totally normal to rely on a guidebook at first. Tarot is a journey, and we all start somewhere!
