To begin reading a book, you need to know the Hebrew alphabet and have a basic idea of how Hebrew works (basic grammar). Then, quite simply, you look up each word in a dictionary and piece the sentence together. I like the online Rav Milim dictionary, which charges a yearly fee.
Let’s practice with a random sentence from the first Harry Potter book.
האגריד שלף שוב את המטרייה הוורודה, נקש בה פעמיים על דופן הסירה, והם התחילו לטוס לכיוון היבשה.
האגריד hagrid – Hagrid. This name you should know through context already.
שלף shalaf – extracted, pulled out.
שוב shuv – again.
את et – you know it’s ‘et’ and not ‘at’ (you, f) because of context.
המטרייה hamitriya – the umbrella.
הוורודה havruda – the pink.
נקש nakash – knocked, struck.
בה ba – (with) it.
פעמיים pa’amayim – twice.
על al – on.
דופן dofen – side.
הסירה hasira – the boat, the rowboat.
והם vehem – and they.
התחילו hitkhilu – they began.
לטוס latus – to speed, to fly.
לכיוון lakivun – in the direction, toward.
היבשה hayabasha – the dry land, the land.
In English, it comes out to approximately:
Hagrid pulled out the pink umbrella again, struck it twice on the side of the boat, and they began to speed towards dry land.
Naturally, this process is slowest in the beginning when you’re first learning. But over time with daily practice, reading will become quicker and more natural. Learning a foreign language to a high level takes a lot of consistent study and practice. Get going!