Here it looks fluffy like whipped cream.
Right when you see it start to change (see picture below - it will no longer be so fluffy like whipped cream), turn the beater speed down to the lowest speed it has. Scrape the sides of the bowl periodically.
As the milk separates out, it will splash up more and more. If you do not have a protection shield for your beater/mixer, hold up a towel or something else to protect you and your surroundings from having a shower of milk.
Here are a few more pictures as it progresses along.
After a while you'll notice it is not changing much. Dump the milk into a jar to save it (this is buttermilk ... great in pancakes, cakes, or whatever). Continue beating on low a little longer to get more milk out; pour off the milk and save.
Now you must wash the butter. Add about as much cold water to the butter as was buttermilk. Beat on low for a bit. Drain. Repeat.
All washed and ready to go. Next beat in some salt. Start with 1t and add more if desired.
The final step is pressing as much water out of it as you can. It works good to kept the butter in the mixing bowl and smash it over and over again against the side of the bowl while tipping the bowl at an angle so the water can drain down. Every so often you'll want to dump the water out so you can see how much new water is pooling.
Press the finished butter into a form or bowl of some kind, cover well and refrigerate. It can also be frozen for long-term storage. 1qt of cream will yield about 1 pound of butter and a pint of buttermilk. Enjoy!