Fill up your jar half way with black coffee beans. Then fill the jar the rest of the way with vodka, leaving a bit of extra room at the top of the jar for shaking.
Add the lid, shake the jar well, label and store the jar out of the way. The coffee extract flavor and aroma will develop over the next few weeks. You can use it as soon as it smells the way it's supposed to, which is usually a few weeks.
Store your extract at room temperature in a dark cabinet.