For example, box 12 has a check box if the cost basis is not reported to IRS, so you will enter it in your return so you will correctly report the gain/loss on the transaction.
In the top of each coded section, it will state what type of code is applicable. In that same section, certain codes tell you that certain items are not reported to IRS.
Form 1099-B is available on irs.gov. Generally, most brokerage houses provide a "substitute 1099-B" to their customers. It looks different but still contains all the same information.
For additional information, there is instructions for how to use each box of Form 1099-B on the back of the copies of the IRS Form 1099-B at the following link:
IRS Form 1099-B copies and instructions
