Confusion

Hello everyone. I'll get straight to the point.

I've been having trouble with particles. "O" and "Ni".
I know that "o" is supposed to mark the direct object and "ni" is translated as to, on, or at.

But my problem is, the book I'm studying from gives and example for using "ni".

Nihon ni itta
I went to Japan.

But since Nihon is also the direct object, wouldn't it be:
Nihon o itta????

I really need the help with this since I know this is just the basic stuff.

Arigatougozaimasu minna.

No, Nihon is definitely not the direct object in that sentence. Direct object is, for example:

- "apples" in "I eat apples," (Ringo o taberu/tabemasu)
- "Japanese (language)" in "I study Japanese" (Nihongo o benkyo suru/shimasu)
- "a movie" in "I saw a movie" (Eiga o mita/mimashita).

The way to think of 'ni' is basically as giving information about the nature of the action, not as defining the direct object of it.
itta.
doko ni?
nihon ni.
Tabeta.
nani wo?
ringo wo.
iwareta
dare ni?
reiko ni.

Like that.

The direct object answers to the quesion ''who'' or ''what'':
What did you eat?
I ate an apple.
Ringo wo tabemashita.

What did you read?
I read a book.
Hon wo yomimashita.

If it doesn't answer the question ''What'', then it isn't a direct object.

Arigatou minna-san! You helped me understand this a lot better!

When you use "o", something is being done to something else.

nihon ni iku

Nothing is being done to Japan, you're just going to it. Expressing movement is one of the uses of ni.

ringo o taberu

Something is being done to the apples, so O is appropriate here.