When I have to use meinem, and when meine?
It depends on the case and the gener. "Meinem" is used when it's Dativ and masculine o neuter, i.e. "ich fahre mit meinem Fahrrad", why? because "mit" is a dativ preposition and "Fahrrad" is neuter. On the other hand, "Meine" is used when it's nominativ or akkusativ with feminime or plural, i.e: "Meine schöne Hose", why?, beacuase it's Nominativ and "Hose" is feminine.