1. When should I use the topic marker 'wa' and when should I use 'ga'?
This won't be the last time you ask this question. Be prepared for a long journey of not knowing, thinking you know, and then finding out that you don't know how to use these two. That said, the topic marker
wa is used to mark old or known information and to refer to general things (like "the sun" or "turtles"). It's usage is sometimes likened to the English definite article "the." It's not the same, but this may help.
The subject marker
ga is used to mark subjects in sentences and clauses. It's always used to mark the subject of relative clauses. Many times it gets the "focus" interpretation; i.e., it marks what comes before it as new information that answers a question. It can also just mark new information in a neutral way. The famous example given for how to use
wa and
ga is the "fairy tale" sentence:
mukashi mukashi, ojiisan ga ita. Ojiisan wa... ("once upon a time there was
an old man.
The old man...").
Wa can also be a contrastive marker, in which it shows that something is being contrasted. For example,
sakana wa tabenai ga, gyûniku wa taberu ("I don't eat fish, but I eat beef").
Also,
ga can mark objects (well, what we would think of as objects). For example, when using
-tai,
ga can mark the object:
gyûniku ga tabetai ("I want to eat beef";
o can also be used) or
anata no koto ga suki da ("I like/love you"). I guess that's enough of an overview for now.
2. Do the Hiragana letters stand for sounds or words? If I put Hiragana letters together, will they form a word out of multiple sounds, like English?
Since consonants can stand alone in Japanese (with the exception of the mora N), all of the kana have a (C)V structure. There are five kana for the five vowels, and everything after that is a consonant plus a vowel, with the exception of ん (mentioned earlier) and を, which was "wo" at one point but the "w" disappeared, leaving just "o."
Aside from the basic kana, some can be altered by adding ゛, which changes the voiceless consonant into a voiced one, like "t" → "d" or "s" → "z" (with some exceptions, one following), and the
ha-gyô can also take ゜, which turns the "h" into "p." The voicing mark, ゛, turns the "h" into "b."
Also, the
i-dan can take small
ya-gyô kana to give palatalized sounds, like
kya, cho (tyo), and
nyu. Then there's the small
tsu, which represents double consonants (
yappari, ippon, kesshin → やっぱり, いっぽん, けっしん).
There are kana lessons at
Teach Yourself Japanese, and also a
hiranaga table and a
katakana table. There is some linguistics terminology there, but you can just ignore it if you want. There should be sound files for each of the kana, too.