To view your coin balance, hover over your name at the top right corner of the homepage and choose "Dashboard" when the menu appears. Your coin balance will appear on the left.
You can earn free coins when you:
Sign up for a Paperless Post account - 25 coins (one time only)
'Like' Paperless Post on Facebook - 5 coins (one time only)
Connect your Facebook account in Account Settings - 5 coins (one time only)
Download and log into the iOS app - 10 coins (one time only)