The SEC writes and enforces rules on disclosure, insider-trading, market-manipulation, and broker conduct. Companies file their financial statements (10-K, 10-Q, 8-K) with it, and those filings are free on EDGAR.
It oversees finra, which handles day-to-day broker regulation. Derivatives on commodities fall under the cftc instead.
Example: a company announces a major acquisition. Its 8-K filing with the SEC, available within days, contains the terms that the press release summarized.
Related: finra, cftc, insider-trading, market-manipulation