I understand both are used to indicate my, however, I’m not sure when to use one over the other
Ma and Mon are a couple of the terms known as possessive adjectives.
Common mistakes with mon/ma/mes, ton/ta/tes and son/sa/ses (French Possessive Adjectives)
The link above will take you through all the various aspects of usage and I recommend that you review the lesson in its entirety to get a thorough overview of this important aspect of French grammar.
Hope you will find this helpful,
I would also add its worth learning the gender of nouns as you come across them. There are a number of helpful guides eg Identifying the gender of nouns by some specific word endings in French Good luck!
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