That's all we do little blue. We don't have a separator etc, we just put fresh milk into a big wide jug or a small milk pail, leave it in the fridge to cool for 12 hours or so. Use a big wide spoon to scrape the cream off the top- do that for a few days until you gather enough. By the time you have gathered enough it's getting ripe enough.
Then as Anke says, shake it until it turns to butter. You can use a hand held mixer to mix it until it turns instead which is slightly easier. Then rinse out with lots of water to get out the buttermilk, and we use wooden paddles to squeeze out the remaining water and to shape it into a rectangle. Add a sprinkle of salt if you want. And remember- it will not be yellow. It comes out white!
Beth