When you read, your eyes look at symbols that stand for sounds, and those sounds represent concepts. Reading requires both of these events (symbols-to-sounds, and sounds-to-concepts) to take place. It happens so quickly, we can ignore the middleman if we want. Writing systems like Chinese are called logographies as opposed to true alphabets, because Chinese characters don't stand for sounds at all, just concepts. You have to learn as many characters in Chinese as there are ideas. English sometimes works like that. Consider the difference between to, too, and two. In this case, different sets of symbols all produce the same sound. The only option the English-speaker has is to memorize separate what spelling corresponds to each idea.
This is a lot of work, and your brain is doing it all the time. It's doing it right now, in fact. On top of that, you don't remember the symbols you've read for the rest of your life. I'm reading a book right now, and I'm in the middle portion, and I don't recall exactly the symbols it opened with, and I'll remember them even less precisely by the time I reach the end. And yet, the thoughts it made me think remain in my head. I still know what the book is about. It's not as though I've never read it.
Now we introduce a third (potentially fourth) stopping pointing in the act of reading: symbols correspond to ideas (through the byway of sounds), but those ideas in turn correspond to an impression. The impression, most often, remains in the reader's mind long after most, or even all, of the symbols and sounds do not. You cannot recreate the physical, indisputable elements of the book, but you can still say what it was about. How can this be?
This is to say nothing of the nuances that exist even within the individual letters and sounds, and how many things even simple combinations can mean. This has been just a little look at the act of reading, provided to you by the act of reading no less.