Learn Russian: Это мамин кулон, я всегда ношу его с собой. - This is mom's pendant; I always carry it with me.

The word мамин is a special possessive adjective formed with the suffix -ин. Unlike regular adjectives, these possessives have a short form in the nominative case. Since кулон is a masculine noun in the nominative case, мамин takes a zero ending. If the noun were feminine, it would take the ending and become мамина.

Why do we use ношу here instead of несу for the word 'carry'?

Ношу comes from носить, which is a multidirectional verb of motion. It is used here because the action is a general habit (always carrying it around), not a single trip in one specific direction (which would require несу). Additionally, носить is the standard verb used for 'wearing' clothes or jewelry.

Why does the sentence use с собой (with oneself) instead of со мной (with me)?

In Russian, whenever the target of an action is the same person as the subject doing the action, you must use the reflexive pronoun себя. Because the subject is я (I) and the person being accompanied is also the speaker, it becomes с собой (with myself) rather than со мной.

Кулон is an inanimate masculine noun. Why is it replaced by его in the second half, rather than staying in the nominative form?