In written Brazilian Portuguese, the possessive adjective is most often always preceded by the definite article. In everyday spoken Brazilian Portuguese, the definite article is dropped and rarely used.
This is in one of the past lessons sort of, with the lesson tu/voce. Here, the internet is cool sometimes: http://answers.yahoo.com/question/index?qid=20070817163506AAZ318k
The first meaning for carta in Portugese is letter. Of course it can have many other meanings. See the dictionary website: http://michaelis.uol.com.br/moderno/ingles/index.php?lingua=portugues-ingles&palavra=carta
In Portuguese, and a lot of other languages, the ending of the word changes for the tense.
Take a look at all the different translations of "ler", which is "to read": http://www.conjuga-me.net/en/verbo-ler
So 'she read' in English is a past tense version of "to read", which in Portuguese has a different spelling almost entirely.
In English, "she reads your letter". We also have some ending changes on our present tense verb. I read, you read, he, she or it reads, we read, you(plural) read, they read
I bet you thought the verb ending was the same for all of them, but third person singular is different from the others. (She read... would be misconstrued as past tense, in which there is no change for this verb. Although past tense "read" is pronounced like red, while the present tense "read" is prounounced like reed.)