Reading books is something pretty useful for learning vocabulary… and enjoying yourself! We acquire lexis. In that way we acquire lexis. It takes rather long to learn a basis of vocabulary. But once that basis is gotten, you can read a book with that tank of words that may help you understand any text.
And then from the context you can understand many other words it’s the first time you encounter. From the context you can understand close to ANY text in the target language, for instance English! It’s like a child reading in his mother tongue. As he grows up, he can read a novel or a tale with new words to him, but from the context he can make out what those words mean, or turning to the dictionary...
And over time he’ll understand more and more and his lexis will be great! A learner when reading books is like a child reading in his mother language. He can face up to any text. I repeat it on purpose and intently: reading is fantastic for learning a language – it isn’t the only skill to exert, though. You become close to a native speaker when still he’s so young but he’s somewhat experienced and like a child reading those books in his mother tongue.
Of course the dictionary is essential. But once you’ve used it for years and gotten a basis of words you can face ANY text – or close to any. Over time you’ve created and made up a nice barrel of terms, a useful one! – At present I’m reading The Hobbit, and I can tell you hereby from my experience. By the way I often use words when writing and posting on my blog and I take and retrieve those words from some part inside my memory and mind: I bring out words from a bottom of words that are correct in English – I guess I’ve learned those words some time and I can produce them from somewhere my inside or kind of that.
So as to finish: in the case of new words you can find out about their meaning from the context, as I said, and also from similar words you may have learned previously. Similar words or words with the same root or derivatives I mean. / Photo from: Bodegas-Palarea-Barricas La Cepa Vieja. On the picture you can see barrels, like the ones we create with words when learning a second or foreign language.