What can I do with skill points? and where can I post questions about duolingo not just the language I'm learning?
Skill points are there as a way for you to measure your own progress, and to let you compare your progress with other users on the site. Your skill points also rank you amongst your friends, creating some friendly competition :).
To ask questions/send feedback about Duolingo, you can use the Feedback tab on the left side of the website. You can also tweet @duolingo or post on the Facebook wall, but the Feedback tab is probably your best bet.