used to indicate the inclusion or accompaniment of something

कुछ का साथ

English Usage: I went to the park with my friends.

Hindi Usage: मैं पार्क गया अपने दोस्तों के साथ।

used to introduce a clause or indicate a specific thing

यह

English Usage: I believe that we can win this game.

Hindi Usage: मुझे लगता है कि हम यह खेल जीत सकते हैं।

refers to a specific person or thing previously mentioned or easily identified

वह

English Usage: I remember that you helped me last time.

Hindi Usage: मुझे याद है कि आपने मुझे पिछले बार मदद की थी।