I am going on a mission trip and I need some Ideas on how to write a letter explaining why I am going and what I am doing. I don't know how to start. Help please!

I need to know to whom you are writing it -- your church, your family, your friends?

Well what type of missionary trip are you going on, medical ? Building a building, teaching them some trade or skill.

Who is supporting the mission

Next who are you writing the letter to, a public announcement, a letter to your parents, your church to thank them??