Problem of particles (wo and wa/ga)

Hi there.

Okay, I'm having a problem with my particles - more specifically, when to use wa/ga and when to use 'wo' in certain situations.

I thought I had 'wo' understood. It follows the direct object of a verb if the verb has one. I know that 'ga' is used for certain things such as 'imasu', 'arimasu' and 'wakarimasu'. A sub question here (not my main question) is why is this, and is there a general rule for it?

Back to it. So I always thought that the direct object was, in the case of eating, the thing being eaten and, in the case of drinking, the thing being drunk. I assume this is still the case but, as I said, there is some confusion. So what, specifically, is this confusion?

Well, I was reading through a Japanese and it had the sentence 'Sushi ga tabetai desu'. So... I mean... so sushi isn't the direct object of the verb here? Then later on, in a different context I heard the phrase 'Anata wo shiritai'. Yeah... huh? How's that working then?

So basically I feel like I'm completely at a loss for what's going on. If someone out there has a nice and simple explanation for what's going on here, that would be great.

Thanks a lot.

I will try and answer. Hopefully someone else more knowledgeable will give a better answer later

So both your example sentences uses -たい which means to want to do something. I want to eat sushi. I want to know you. Something like that.
And from what I know when you use the -たい conjugation, if you usually use を you can also use が instead.
If there is some difference in nuance I do not know.

"Ga" usually indicates the subject, but also can indicate the object of some groups of verbs, including the -tai form as staren-san mentioned.

examples of verbs/adjectives that take "ga" as the object marker
state verbs; wakaru, iru(to need), dekiru,,,
potential forms/-tai forms; taberareru, tabetai,,,
adjectives(the ones which express emotion/sense); sukida, jouzuda, nikui, hitsuyouda,,,

As for "Anata wo shiritai", "Anata ga shiritai" is also OK, but "anata" could be misinterpreted as the subject of "shiritai". So, "anata wo" would be preferred over "anata ga".

Ah, this has been most informative guys. Thanks for your help.