Stand on your skateboard with your back foot across the tail and your front foot right behind or on the bolts for the front trucks. This is a basic ollie stance, and is used for a huge number of skateboarding tricks.
Now, bend your knees and keep your shoulders level above the skateboard deck. Relax. Breathe normally. Stop freaking out.
Next, shift your weight to your back foot. Not all of it, maybe about two thirds. As you shift your weight to your back foot, bring your front foot up a little. The more you shift your weight to the tail of the board, the more the nose of the board will want to pop up into the air. Try balancing on just the back wheels, just for a moment. It will feel scary, like you are going to fall. Maybe you WILL fall! Don't worry about it, just relax and get back on your board. See how long you can balance on those back wheels.
Once you've done this for a while, we can move to the next step:
