The parts of speech in Japanese are nouns, pronouns, verbs, adjectives, adnominal adjective, pillow words, adverbs, auxiliary verbs, particles, conjunctions, prefixes, suffixes, and interjections. There are so many different types that it takes time to fully understand them, but I will give you some examples and explain them bit by bit.
わたしは水を飲む。 - Watashi wa mizu o nomu.
I drink water. [ENG]
Classify this sentence according to parts of speech.
わたし - noun
は - particle
水 - noun
を - particle
飲む - verb
In Japanese, there is a part of speech called a particle. For example, there are no particles in English. I think that particles are difficult for many foreigners to understand.
We will not think about particles right now. Then the sentence is as follows.
わたし 水 飲む。 - Watashi mizu nomu.
If you say to a Japanese person, "Watashi mizu nomu", most Japanese people will think it's an unnatural sentence, but they can actually understand the meaning. In other words, simple sentences can be understood without particles.
A very important point here is word order. For example, in English the sentence is as follows.
I drink water.
[Subject - Verb - Object]
On the other hand, in Japanese, the sentence is as follows.
わたし 水 飲む。 - Watashi mizu nomu.
[Subject - Object - Verb]
This is a very important point.
When studying Japanese, the first thing to do is to correctly understand the word order in Japanese. In many cases, sentences can be constructed by adding particles after the subject or object.
It can be confusing at first as to which particles to add, but there are some set patterns that need to be understood.
Here's another example.
わたしは東京に行く。 - Watashi wa Tokyo ni iku.
I go to Tokyo. [ENG]
Classify this sentence according to parts of speech.
わたし - noun
は - particle
東京 - noun
に - particle
行く - verb
Here again, we will not consider particles. This will result in the following sentence.
わたし 東京 行く。 - Watashi Tokyo iku.
This is also unnatural, but most Japanese people will understand the meaning.
There is one difference from the previous example: in this example, the preposition "to" is present because "go" is an intransitive verb.
In English, transitive verbs don't need prepositions, but intransitive verbs do. In Japanese, both intransitive and transitive verbs need particles. In Japanese, particles function as prepositions. Prepositions don't exist in Japanese.
Not only verbs, but also particles are necessary after subjects. As mentioned earlier, the meaning is often conveyed without particles. Particles act like glue to attach to subjects, verbs, etc.
When studying Japanese, first think about the word order, then think about which particle is appropriate to use.