What's difference between garment and clothes
I believe these two words are more or less the same but I am wondering is that one formal the other one informal? or like Garment is old-fashion way to say it?

Question

Answer

There's also a grammatical difference. 'Clothes' is a plural word. It has no singular form. Shirts, dresses and jeans are clothes.

But try to complete this sentence with one word: 
"My blue velvet skirt is my favourite ........."

Favourite what? Not clothes. Not cloth. Not clothe. Those words don't fit. But you can say 'My blue velvet skirt is my favourite garment'. We don't use the word 'garment' very much, but it is useful, because it has a singular form.

Answer

Basically, your right ???? garment seems more old fashioned and is less commonly used.

Não perca a oportunidade de aprender uma língua no conforto da sua casa. Navegue pela nossa seleção de professores de línguas experientes e inscreva-se na sua primeira aula agora mesmo!