Transmission89,
You won't be able to add the descriptions by editing anything in the .pak. You can use the skills library and create the basic skills as you did the advanced skills. Once completed you can drop the links from the skills library onto the basic skill list. I don't have the description active in the built in basic skills due to copyright issues.
The missions library is for building "quests" and having the experience points they are worth generated ahead of time. Once a mission is started, drop the mission into the Party Sheet, you can award the xp directly to the PC's from there once they complete it.