How do I say 'just now'?

The 刚才 / 刚 / 刚刚 family lets you fine-tune exactly how recent “recently” is:

• 刚才 — a moment ago. Could be 30 seconds or 30 minutes. It is a noun referring to the recent past moment: 刚才的事 (the thing that just happened).
• 刚刚 — just now, within seconds. Stronger recency than 刚才. 我刚刚到 means you are probably still putting your bag down.
• 刚 — the short adverb form, placed directly before a verb. 我刚吃完 (I just finished eating). This is the most efficient and common in fast speech.

The grammatical distinction is the hidden trap: 刚才 can stand alone as a time reference (刚才 = just now, as a moment in time), while 刚 must attach to a verb. Saying 刚 without a following verb is incomplete. The doubling in 刚刚 adds emphasis but follows the same adverb rule as 刚.