It's difficult to begin right off the bat at something new. For me personally, I am a very hands on learner, so by visually seeing and working through an activity, I can achieve a greater understanding of what I'm working towards. That being said, templates are a guide, not a mandatory format, so take these examples with a grain of salt, and definitely make sure to personalize what you write.
TO AN ELECTED OFFICIAL
When writing a letter to an elected official, the best way to find a form a contact is through their website. Some elected officials only allow residents in their districts to send them anything, but others may be more open to mail from anybody. However, you should start with someone more locally because they'll be able to address your issue more efficiently and effectively.
Determine why you are writing to that elected official. Do you want them to respond to you? Do you want to plan a meeting? If so, make sure to include your email so they can respond to you more quickly, and make sure to give a little bit of background on yourself! It doesn't have to be too extensive, but at least have your name and age/grade.
TO AN ORGANIZATION
When writing a letter to an organization, you probably have already seen their website since you found them in the first place.
Determine why you are writing to that organization. Do you want to learn more about their work/their issue? Do you want to volunteer? Do you want to begin your own branch? If so, list some prior experiences you have accomplished that relates to their work. That way, they can have an idea of the places in which you'd be the best fit for in their organization. Exemplifying your interest and connection to the issue will show that you are dedicated to the cause.
By writing letters to different organizations and representatives, you are able to make beneficial connections to positively impact your community and your specific topic. You get to act on your values as well as practice self-advocacy