Slit: On a cutting board, hold the stem-end of the vanilla bean with your finger. From there make a lengthwise slit with a sharp knife along the entire length of the vanilla bean.
Split & Scrape: Still holding the stem-end down, flatten the bean open as you scrape out the paste of seeds with the knife, starting from the stem all the way to the very bottom.
Use the vanilla seeds immediately.
For the leftover vanilla pods: You can submerge them either in a jar of sugar to store and infuse your sugar with a vanilla scent, or in jar of alcohol (vodka or Bourbon) for your own vanilla extract. Or you can roughly chop them and then grind very fine in a coffee or spice grinder, and use half a teaspoon as a substitute for a teaspoon of pure vanilla extract.
Notes
If you only need to use half of a vanilla bean, cut the bean crosswiseinto two halves first, so that you can store the unneeded half intact.
Variation: You may find it easier to cut the bean pod (or segment) completely in half lengthwise, and then scraping out the seeds of each side separately.