"cartinha" it's a litter letter, but bigger than a note. You can start with "Querida família" or "Meu querido"(for love letter) "Sinto saudades de vocês" (I miss you all) "Eu estou bem" ( I'm fine, I'm ok) "Como você está?" (How are you?) "eu te amo" (I love you) "Espero vêr você logo"(I wish I could see you soon)

what do you want write ? maybe, you could write something like : Oi (hello) tudo bem com voce ? espero que sim! (is everything fine with you ? i hope so) estou escrevendo para praticar o meu portugues (i´m writting to practice my portuguese)

wiki.familysearch.org/en/Portuguese

Olá ! About for family letter and love letter. I can't understand many Portuguese word, but I will try to write in Portuguese. Short sentence is Ok like cartinha. I don't know well about cartinha, my image is small letter. I read about it by a book. Can you explanation about cartinha?

Olá, bem-vinda. Que tal formular sua pergunta em Português?