The particle の is one of the easier particles to learn. Its most basic use is to denote possession, e.g. my bag, her shoes, their parents. It is also the only basic particle that defines the relationship between nouns rather than between the noun and the verb.
これは 財布です。
This is a wallet.
これは 私の財布です。
This is my wallet.
Note the order in the second sentence. The possessive particle follows the pronoun. In this case, the pronoun “I” followed by the possessive creates the same meaning as “my” in English—there is no separate word for “my” in Japanese. The same applies for his, her, our, and so on.
This is fairly intuitive when thinking about simple possessive sentences (my wallet, her friend, etc.); however, the particle can also be used in a slightly more abstract sense.
その 女性は 会社の社長です。
That lady is the CEO of a company.
Here when thinking about the Japanese grammar we have to consider it in terms of the “CEO belonging to the company” or the “company’s CEO”.
それは 私の携帯です。
That’s my mobile phone.
彼の お父さんは 学校の先生です。
His father is a school teacher.
In the last example sentence the possessive particle is used to modify the topic of the sentence and thus becomes before the topic particle.
私の名前は オリバーです。
My name is Oliver.
We can also use の directly with the auxiliary verb when the noun is known by both speaker and listener.