I am a beginner of cooking. I know there is no clear-cut for this question after research on Google.
I did shopping today at a large local supermarket but shockingly, there are lots of butter/margarine but none of them has the word "butter'' or ''margarine'' on any parts of their box. They use the word ''oil'' instead but I am pretty sure that they are either butter or margarine.
By the way, there are so many choices, what should I pay special attention to on the nutrients labels? Thanks
Where are you situated, Kenny?
Butter is made from cream and nothing added except, sometimes, a little salt. If it has any other ingredients or references to preservatives it isn't butter. There are two types of butter - sweet cream and lactic. lactic butter (eg Danish butter) has a small amount of "ripened" butter in it but it may not say this on the ingredients (it doesn't in the UK but it depends on the labelling regulations where you are).
There are other butter substitutes which are a mixture of butter fat and oil and other things, which purport to be "better" for you than butter and in some cases are lower in fat (usually this is achieved by adding water and other things) but, as you say these are not butter and (at least in the UK) they have to be called "spreads".
There have been some recent studies published which claim that butter is not as bad for us as has been painted but I don't know where this originated (it may have been paid for by the dairy industry!). As a non-scientific person I am inclined to believe it (because I can if I want to
) and butter tastes better. To the best of my knowledge British dairy cows can't be given hormones to encourage milk production but I believe this may be allowed in some countries. Depending on where you live, you may choose to eschew butter for that reason.
As regards margarine, you rarely see the word in British shops although it is sold in Britain (eg the product which used to be labelled "Stork Margarine" is now just "Stork" and Tesco own brand Margarine is now just labelled "baking fat" which sounds very unappetising).
Personally, I prefer to stick with my butter and moderate my consumption. I prefer the taste and "feel" of it on my bread and in baking too although I'll use margarine for a strongly flavoured cake such as gingerbread if I'm short of butter. However, if frying with butter it is a good idea to add a little blandly flavoured cooking oil as it tends to make the butter less likely to burn.