In English we say my mother and my father. In French you'd say mon père and ma mère, because words like my and your change based on the gender of the word after them!
| masculine | feminine |
|---|---|
| mon père my father |
ma mère my mother |
| ton frère your brother |
ta sœur your sister |
| son fils his / her son |
sa fille his / her daughter |
In English, we say Marie's cat. But in French, you'd switch the word order and say le chat de Marie.
Before vowels, de becomes d'.