You can use paypal or your credit card to obtain kreds. You can get 50 kreds for $5, 110 kreds for $10, or 225 kreds for $20. This is the what kong staff had to say about the release:
Have you ever had more love for a particular game than a simple 5/5 could express? Well now there's a more concrete way to say thank you: a tip jar for developers. At the same time Ron Paul's dream of competing U.S. currencies has finally come to fruition today with the launch of kreds, the official monetary system of Kongregate. Using now-obsolete United States dollars, Kongregate players can fund their accounts using a credit card or Paypal. Once your account is funded, you can use kreds to tip developers on the site using our shiny new tip jar system. Hey, if you're willing to fork over a few dollars to a waiter for carrying over your omelette, why not show some love for the talented developers who slave over a hot ActionScript stove to bring you some really great games for free? Once a tip has been made, your profile will be optionally updated to show your contribution and support. After credit card fees are factored in, 100% of the tip revenue will go straight to the developer, without any cut for Kongregate (it's okay, don't worry about us -- we have lots of ramen).
So if you feel the need to support a developer (like myself) then buy some kreds and show them some love.