Here are some examples:
* slow (adjective) + -ly = slowly (adverb)
* quick (adjective) + -ly = quickly (adverb)
* happy (adjective) + -ly = happily (adverb)
While there are a few exceptions to this rule, generally, the "-ly" suffix signals that the word is an adverb, which modifies verbs, adjectives, or other adverbs.