"Salted butter" and "unsalted butter" are sold when you go to the dairy section of the supermarket.
There are also shops that sell fermented butter.
"Unsalted butter" (salt not used)
Since it doesn't contain salt, you can adjust the overall saltiness yourself, but it doesn't keep well.
Unsalted butter is excellent in that you don't have to worry about the amount of salt when using a large amount of butter for sweets and the like.
"salted butter"
1-2% of salt is added to the weight, and it is highly preservable.
Salted butter can be spread directly on bread or used to flavor dishes. If you add a large amount to sweets, etc., the salty taste becomes stronger.
"fermented butter"
The fermentation process of lactic acid bacteria produces various taste and aroma components, so butter has a unique aroma and richness.
Because it has a unique flavor, it is used when you want to add richness to sweets and dishes.