thanks crontakz! someone already explained it for me yesterday in another discusstion,and this is a copy of his post, hope this help!
Mon is masculine and is used when the object is masculine. Ma is feminine and is used when the object is feminine. They both mean my. Le cheval the horse masculine ......Mon cheval = my horse La soupe the soup feminine .....Ma soupe = my soup
In French, adjectives have to align in gender and number with the nouns they are describing. For nouveau, here are the different forms:
For singular masculine nouns, you use "nouveau" ("un nouveau livre") or "nouvel" if in front of a noun that starts with a vowel sound ("un nouvel hotel").
For singular feminine nouns, you use "nouvelle" ("une nouvelle robe").
For plural masculine nouns, you use "nouveaux" ("des nouveaux livres," "des nouveaux hotels").
For plural feminine nouns, you use "nouvelles" ("des nouvelles robes").
Hope that clears things up!