I can't see how old your comment is because I'm on the app, so sorry if I'm responding years late.
In English, you normally use "a" when you're talking about things that it is possible to count. For example, you could say "a house" or "a dog."
You can't say "a butter" because you can't count butter. But you can say "a stick of butter" because sticks of butter are discrete, countable objects. It would also make sense to say something like "a pound of butter" or "a kilogram of butter."