Learn Swedish: Halsduken är av silke. - The scarf is made of silk.

In Swedish, you don't need a verb like 'gjord' (made) in this context. The preposition av on its own is used to express material composition. Saying är av silke perfectly captures the English meaning 'is made of silk'.

How does the word halsduken break down?

It is a compound noun made of hals (neck) and duk (cloth). The -en suffix makes it definite, so it literally translates to 'the neck cloth'.

Can I use silke as an adjective, like saying 'en silke halsduk'?

No, Swedish doesn't use material nouns as separate adjectives the way English does. You either use the preposition av as in this sentence, or you combine the words into a single compound noun like silkeshalsduken (the silk scarf).

I sometimes see the word siden for silk. What is the difference between silke and siden?

Both words translate to silk, but silke refers to the raw material or the spun thread, while siden refers to the finished woven fabric. For clothing, you will actually hear av siden very often, but av silke is also correct and emphasizes the raw material it consists of.