I'm new to this and would like to know how to start up a quest with a courier delivered letter. The letter has already been made, but I have know idea how to get the courier to bring it to the player. Any help is appreciated.

Look into AI Packages. You will add a Travel package to the AI Packages tab of an Actor. If you right-click > Add > you'll see a bunch of "default" packages that you could try like "defaultTravel...". Then just fill in the blanks. Or you can make your own.

http://www.creationkit.com/Package
http://www.creationkit.com/Travel_%28Procedure%29

If you can remember this happening in-game at some point, you can open that Actor in the CK and see how it was done.

Thanks, I'll keep trying things out