When you get a comment on your den page saying Paws Up, what does itbmean? How do you reply to it when you're new? Or is it only premium players who can leave comments on den pages?

It means someone 'paws up'd your pack and left a comment saying they did. You can leave a comment by clicking comments and then add comment. Sadly, you can't really reply directly, but you can a comment in their shoutbox too. Or PM them, maybe catch them in chat.

Hope this helps