This is the 2nd most frequent Chinese word.
的
"的" is a possessive or attributive particle indicating ownership or modification.
In this sentence, '的' is used as a possessive or descriptive particle to connect the adjective '可爱' (cute) with the noun '小狗' (little dog), forming the phrase '可爱的小狗' (cute little dog).
这是一只可爱的小狗。
This is a cute little dog.
'的' here indicates possession, connecting '我' (my) with '朋友' (friend) to express 'my friend' ('我的朋友').
他是我的朋友。
He is my friend.
Within this context, '的' combines '我' (my) with '想法' (thoughts) to denote possession, forming '我的想法' (my thoughts).