[prowsnobswend]

You've just answered your own question. If you know the vocabulary, then you can easily tell which words are which. And Hebrew does sometimes have vowels or vowel-like sounds written (the yod or alef letters, e.g.).

Is ths sntnc hrd t ndrstnd wtht vwls? Prbbly nt.

Hebrew books that are intended for children or Hebrew learners, however, often use special marks for indicating vowels, which is convenient until you get used to reading without them.

Hebrew has a fairly simple grammatical structure. How hard it is to learn a language always depends primarily on the person in question, but Hebrew is somewhat simple to learn. Although it naturally has a somewhat frustrating start to learning it, as when you're just beginning, you can't read most words.