Wording is important when you're writing a letter, especially if you're trying to carefully word a request. If you're looking for financial relief or forgiveness, I have new hardship letters and apology letters. If you simply want to thank someone, there are plenty of new thank you letters.
In Illustrator, you can design patterns, complex graphics and work with type. You can learn to design printables fast with the Basic Printable Design Course from Printable Crush. Illustrator is a highly in-depth program, so taking a course is a quick way to learn the basics.