Fredrik, The quick answer for a normal workout is to perform the Crossfit Warmup followed by the Workout of the Day, scaled to your current fitness level. The detailed answer is open and print out the FAQ Section, the free copy of Crossfit Journal and Start Here. These have the info you need.
When I started CF, I had been doing "old school" weight training. The rapid paced,intense anarobic approach to exersise called for in Crossfit made the Warm Up seem like a complete workout at the beginning. Start slow, proceed at your own pace and enjoy.