I need to find information on this, sometimes it is hard to understand. What I am looking for is a way to practice m+f , I don`t know were to go?
when to use masculine or feminine
There are two distinct problems faced by the language learner. !) Given a (correctly) written noun in Spanish, can you determine its gender from the form of the noun? The answer to this is, usually (the previously cited article suggests some general rules). There are, of course, exceptions. 2) If, on the other hand, your point of departure is (say) an English word, such as "table" and you're asking yourself, "should it be "meso" or "mesa", all bets are off. Grammatical gender has almost nothing to do with natural gender (sex). The most obvious cases of a real relationship relate to people and animals (at least those with which humans normally interact (rooster/chicken, bull/cow male dog/bitch, etc.). In dicussions of poetry (at least, in English and, probably, in Spanish, one can find references to masculine/feminine rhymes. Again this has nothing to do with sex but, rather, to the classification of some sounds as masculine/feminine.
Movie dialog such as Governor Arnold Schwartznegger's "No problemo." do not, of course, help matters.
The mnemonic that I was taught was for the masculine endings "loners" and for the feminine endings "d-íon-za".
Here's an article on gender.