Learn Dutch: Zulke hagel is natuurlijk erg gevaarlijk. - Such hail is of course very dangerous.

The word zo'n is used for singular, countable nouns, meaning "such a". However, hagel (hail) is an uncountable noun, just like water or sand. For plural nouns and uncountable nouns, Dutch uses zulke (such).

I learned that erg means "bad" or "terrible". Why does it mean "very" here?

When erg is used as an adjective on its own, it indeed means "bad" or "terrible". But when it is placed directly before another adjective like gevaarlijk (dangerous), it acts as an adverb meaning "very". In this sentence, it means exactly the same thing as heel.

How do you pronounce the -lijk ending in gevaarlijk?

The suffix -lijk is always pronounced like "luk" with a short, unstressed "u" sound (a schwa). Even though it is spelled with the vowel combination ij, the word is pronounced "ge-VAAR-luk".

Could I put natuurlijk at the very beginning of the sentence?

Yes, but remember that Dutch uses "verb second" word order in main clauses. If you put Natuurlijk in the first position, the verb is must come immediately after it, pushing the subject to the third position. It would become: Natuurlijk is zulke hagel erg gevaarlijk.