Particals

The particles in Japanese are very important. They connect the words to each other, labeling the words and dictate the tone of  the sentence. I think the particles are the key to understanding Japanese. You can't know all the words, but you can learn the particles and understand the main idea of the sentence.
In this post I'll write about the main particles (appearing frequently), but if you want the full list of them, you can find it here.

General rule
Typically, in Japanese writing there are no spaces between the words. But when they write with spaces (books for children) , the particles always stick to the end of the word.

Wa(は)
When apearing after a word, indicates that this word is the main topic of the sentence.
Note: the syleble  は typicly pronounced as ha, and only while used as a topic maker, pronounced, like wa.
example:
Watashi wa neko desu. (わたしはねこです) I'm a cat.

Ga (が)
When appearing in the end of the sentence, indicats an open ended sentence (not finished sentence).
example:
Kono nekoga (このねこが...) This cat...

Ka (か)
When appearing in the end of the sentence, turning it to a question.
Note that the structure of the rest of the sentence not changing.
example:
Neko desu. (ねこです) It's a cat.
Neko desuka (ねこですか) Is it a cat?

No (の)
This particle is used to expresses possession or a relation between two nouns.
example:
Watashi no neko desu. (わたしのねこです) It's my cat.

Ni (に)
This particle indicates derection.
example:
Watashi wa tomodachi ni ikimasu (わたしはともだちにいきます) I'm going to freand's house.

Ne (ね)
When appearing in the end of the sentence, turning it into an agreement seeking sentence.
example:
Neko desu. (ねこです) It's a cat.
Neko desune. (ねこですね) It's a cat, isn't it?

Yo(よ)
When appearing in the end of the sentence, working not exactly like exclamation mark, but indicates a strong conviction.
example:
Neko desu. (ねこです) It's a cat.
Neko desuyo. (ねこですよ) It's a cat!