刚刚 (gāng gāng) is an adverb meaning 'just a moment ago,' placed right before the verb to say an action happened very recently. It is very similar to 刚 (gāng, HSK3), but 刚刚 can sound a bit more emphatic or recent. Unlike 刚才 (gāng cái, HSK3), which is a noun referring to the immediate past time (e.g., '刚才的事情'), 刚刚/刚 are adverbs that directly modify the verb.