Quick answer
Wisdom is not just knowing things; it is knowing how to hand them over. The wise make knowledge good in the telling. Fools spill.
Read both lines
The contrast is between craft and leakage. The Hebrew behind "uses knowledge rightly" says the wise tongue makes knowledge good, which assumes something worth noticing: the same true fact can be delivered well or badly, and delivery is part of wisdom rather than a decoration on it. The second line supplies the opposite motion. "Pours forth" is bubbling-over language, the mouth as an unattended pot, output without judgment about timing, audience, or amount. Plenty of foolish talk is not false. It is simply everything the speaker has, released at once, on whoever happens to be standing there.
Related: Proverbs 15:23 · Proverbs 15:28 · Proverbs 12:18
New King James Version®, Copyright © 1982, Thomas Nelson. All rights reserved. Full copyright information. Scripture provided by API.Bible.
Go Deeper
If this verse has been used to put weight on you that it was never carrying, ask about it directly.