As with writing a letter in English, it is important to adopt the correct register and tone for the person you are writing to. To open your letter, use one of the following options picking the best one that suit the tone of your letter. Querido.... this translates as Dear.....: It is informal in Spanish and so should only be used with people such as friends or family. It is important to chnage the agreement of Querido to suit the person querido for a male and querida for a female and queridos for multiple people. If you want to write a more formal letter you are going to start with Estimado.. ,Estimada... or Estimados... In this letter you are going to write in the informal form because you are asked to write to a friend. In the body of the letter it will be a good idea if you mentioned what you did with your family or friends to celebrate your last birthday?-Que hiciste con tu familia para celebrar tu ultimo cumpleaños? You should answer what your friend is asking: Tell him about your college and how is it going.- Tus opiniones sobre tu vida en el colegio. Tell him how are your exams going and also tell him about your plans for the future. - Como te van los examenes y tus planes sobre el futuro? What are you going to do when you finish college?-Que vas a hacer cundo terminas el colegio? It will be a good idea to ask how was his birthday what did he do with his family and how is he?- Que hizo el para celebrar su cumpleaños y como esta el? To conclude the letter there are many options that you can be chosen to finish it like: Un abrazo- a hug, Besos y abrazos-kisses and hugs, cariñosos saludos- affectionate greetings.