If people knew how easy it is to make butter, it would be impossible to sell in the store - home made butter is both a LOT better & a LOT cheaper.
(Note that the best store bought butter I know of is Lurpack from Denmark and it is nearly as good as home made, however it comes at a premium price).
Then I was a kid I actually made butter by accident using only a hand whipper while trying to make whipped cream. At that time I saw it as a failue - too much whipping. However, that is exactly how you make butter : whip it a little more and the whipping cream will part into buttermilk and butter.
Buy 1 liter of whipping cream and prepare a bowl.
Pour all of the whipping cream into the bowl
Start whipping and continue whipping.
Keep whipping until the cream parts.
You can see the buttermilk and the butter.
Garbage the buttermilk (buttermilk does have uses, however I just garbage it) and you are left with the butter.
After massaging the butter a little.
Pack the butter in appropriate sizes and store it in the freezer (there it is good for half a year). Have some of it in the refridgerator there it is good for about a week.