A header rather than a saying, and one of the clearest places where the Bible describes its own assembly.
Quick answer
A new collection begins, and the verse tells you who gathered it: scribes working for King Hezekiah, roughly two and a half centuries after Solomon. The Bible is describing its own editing, out loud, in its own text.
Read both lines
The line is administrative and that is what makes it remarkable. Someone in Hezekiah's court went through older material, selected from it, and copied it forward, and the book preserves the credit rather than hiding the seam. Scripture does this more often than readers notice, and here it is unmistakable: proverbs of Solomon, copied by the men of Hezekiah, with both facts stated in one breath.
What that does for a reader is remove a false expectation. This book did not arrive in a single motion, and it never claimed to. It was collected, arranged, and passed along by people who thought the material was worth the labor, and the God who inspired it worked through that labor rather than around it.
Related: Proverbs 1:1 · Proverbs 10:1 · Proverbs 24:23 · Proverbs 30:1
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.