First, Japanese text generally doesn't have spaces between words, or markers to show the end of a sentence (some writers will use "." "," and "?" But not everyone does.) So, the question becomes, how do we know how to parse a sentence? I don't think there's a clear rule for this. After practice, I just eventually learned how to tell where one word ends and another begins. The ending of sentences tends to be a little more obvious in that the next sentence often starts on a new line.
Second, verbal punctuation. While many writers now use "?" at the end of a sentence, it's still common to see "ka", which is the sentence-ending question particle. "ka" is also used in spoken Japanese to indicate a question. Additionally, a small "tsu" (っ) may be used to indicate emphasis or surprise, such as in "na-ni--!!" (なああにいいっっっっ) (nani = what). The "tsu" acts like an exclamation point, but isn't actually verbalized in conversations. Notice also here that the vowels in "nani" are being stretched out as well.
Third, verbs. In Japanese, verbs generally consist of one or two kanji followed by some hiragana. The hiragana is used to show tense and passive/active voice. The problem here is being able to tell when a string of hiragana is used for a verb, or if they include a handful of standalone particles. Again, you pick this up through practice.
食べる - Dictionary form of "to eat"
食べます- Polite form of "to eat"
食べました - Polite form of "ate"
食べません - Polite form of "won't eat"
食べなかった - Polite form of "didn't eat"
食べなかったが - "didn't eat" followed by the particle "ga", meaning "didn't eat, but..."
The last example should be parsed as two words, as "食べなかった が,..."
Fourth, politeness. Japanese culture is tightly intertwined with the concept of being polite to strangers and to people of higher social ranking than yourself. That is, there is a set of words to be used when talking to a stranger, a customer, your boss, or your seniors at work; and a different set for speaking with close friends and family. These words have the same meaning ("de gozaimasu" and "desu" both mean "is") but one is more polite than the other. This just means that you have to be able to recognize when a character is being more polite or not, which can be a great insight to the relationship between characters, but it adds to the number of words you need to study.
Fifth, sentence structure. The verb-noun format is generally reversed between English and Japanese (not always, though). "This is a pencil" becomes "kore wa empitsu desu" ("this a pencil is"). In more adult speech, sentence structures can get really convoluted, which is why I'm writing these blog entries.
To be continued...