Use a sharp knife to slit your vanilla beans. No need to cut them completely, you just want to release some of their essense. Place them into your bottle or jar and pour your alcohol of choice over the top.
Seal your bottle up and give it a shake. Store it in a cool dry place to "brew". Occasionally give it a shake to encourage a delicious vanilla extract.
Your vanilla extract will start to have flavor at about 8 weeks, but will be the BEST after 6 months +.
Your vanilla beans are reusable. As you use your vanilla extract, pour some additional vodka, or alcohol of choice back in the jar. Give it a little shake. As you begin to use your vanilla, you can refill with a little vodka each time. This will keep a constant brew and you will always have plenty of vanilla for baking.
Just make sure you are using a gluten free alcohol; Many vodkas are.