Chinese does not use a word separator. How a novice learner can detect the word's boundaries?
You can only detect word boundaries by the context and your vocabulary. If you don't know words many enough or the situation at hand much enough, there isn't much other way to ensure you understand the things correctly.
The reason that Chinese doesn't have word boundaries is that there are "character boundaries". In English, the basic unit of the lexicon, called a lexeme, is one word separated by spaces or punctuation. In Chinese, the lexeme is one Chinese character, so rather than having separated words, it is easy to distinguish different characters in a sentence. However, the hard part is that many Chinese words are actually multi-character words, much like multi-word terms / phrasal verbs in English. If English were to use multi-word terms as frequently as does Chinese use multi-character words, new English learners will find it equally hard to learn English.
Today over at LanguageLog, I came across this sentence:
Inadvertently, when scanning that phrase I ran down a gardenpath (yes, that's what linguists call it: a fruitless attempt that turns out to be the wrong choice, so you have to back up). Turns out it's not 開發 中國(家) *"develop China's (state)??", but, rather, 開發中 國家 "in-development states" (i.e. "developing countries").
Such things will happen and happen again to the reader, and if you care to know more, head over to said site and google it for 'gardenpaths', there's lots of examples for a number of languages. Just the other day I realized German "Maisturm" is ambiguous: is it "Mais-Turm" (maize/corn tower) or "Mai-Sturm" (May tempest)? Probably the latter in most cases, but only context can tell.
I remember some of the beginner's textbooks for Chinese using spaces between words, so I guess you'll still be able to find some. As for why spaces are not normally used in Chinese and Japanese (but in Korean), one can only guess that people find them too unsightly, not really needed and maybe too big a change from what they're used to.
Also, while extra spaces might benefit the reader, they do put a burden on the writer (try to add them while staying consistent—it's not easy!).