cut the beans in half so they fit into your chosen container and score them lengthways so as to expose the seeds.
put them in a sealable glass container (I used a 125ml amber glass medicine bottle) and cover them with vodka or ethanol, shake and store away form heat and sunlight.
Shake the bottle every now and then. The extract will be ready to use after 6-8 weeks.
Notes
Your home made extract will get better the longer it is stored, smelling and tasting less and less alcoholic as time passes. It can be kept indefinitely and topped up as and when with alcohol and more vanilla beans.