Butter is a firm fat that’s made by churning (agitating) cool cream. Cream, its unadulterated state, is an emulsion of fat within water: little butterfat globules within thin lipoprotein membranes, suspended within a watery medium. The act of churning breaks most of those membranes allowing the butterfat — a mix of different types of triglyceride molecules — to flow out.
At that point some very interesting things happen. Groups of like molecules start to collect and stack up on one another, forming crystals. The crystals collect into large masses and when the masses are pressed most of the rest of the watery medium (known as buttermilk) is expelled. The result is a reverse of the original emulsion: tiny drops of water within a medium of fat crystals, free fats and a few remaining butterfat globules.
It’s this mixture of different fats in different forms/phases that gives butter its semi-firm consistency. If butter were composed entirely of uniform fat crystals it would be hard as a rock. The structural variability gives butter a softer texture as well as “broad” melting point. That is, it melts steadily and slowly as opposed to all at once, as the various crystallized fats in the mix — which all have different melting points — go from solid to liquid. On average, butter melts at roughly 90 degrees Fahrenheit, though that can vary depending on the brand, time of year, etc..
So butter is extremely variable stuff, whose flavor, color and consistency change depending on the breed of cow, diet of the cow, location of the dairy farm and time of year.