Add milk kefir grains to a large jar (size depends on how much milk kefir you want to make)
Fill with milk, leaving about 1 inch head room at the top.
Stir, cover with a lid and allow to sit for 24-48 hours. The exact time will depend on the room temperature in your kitchen, and the activity & maturity of your grains.
When the kefir reaches your desired consistency, strain through a metal strainer into a large bowl.
Transfer the kefir grains left in your strainer into a fresh jar, and fill with milk.
Store your finished kefir in the fridge until ready to use.