I'm not sure what you're asking in the second line, but I'm pretty sure the answer is "no." It's about learning vocabulary, just like it is in any other language. 'shigoto' is written 仕事and read しごと, that's that, and that's how you memorize it(note that this particular word is made up of an on + kun). You don't need to divine it through the kanji. The kanji are helpful in remembering, and can help you guess, because they do have readings that are more frequent than others. But you need to remember words as words. Remember that 仕事 = しごと and しごと = 仕事 the same way that you remember the word 'work' in English. work = w o r k, w o r k = work. It's not as different as people like to make it out to be, especially from English, which is honestly made up of phonograms that are only about as phonetic as the kanji are. How do you know to read 'ow'? Well, in cow, it's this way, and in row, it's this other way. Unless you mean a British 'row,' as in a fight, in which case it's that first 'ow' again, apparently. Right? Right. The Kanji just make it harder because there's so many of them and they're unique, but also easier because they're unique (!) and actually have meaning inherent to them.
As for when you use kanji, as opposed to kana, you use them all the time. They form the core of the writing system. The only parts of speech that aren't written with kanji as a
rule are particles and the inflecting portion of inflecting words (verbs, adjectives). Also many foreign words are in katakana, but that's not really a part of speech. Other individual words may or may not be written using kanji, but it doesn't have to do with their role as words, it's largely arbitrary - many words have kanji, but are often written without them, and some words have no kanji at all. So, yes, names, titles, as well as all other nouns, adjectives, verbs, adverbs, everything that isn't a particle or a conjugation may be written with kanji. But they may also not.
More information:
http://en.wikipedia.org/wiki/Kanji
http://en.wikipedia.org/wiki/Japanese_writing_system