That amount is taxable at a rate based on your current income tax bracket. Your broker has no way of knowing your bracket, so can’t calculate a tax.
No, it means this is the amount of interest income you will add to your tax return on the line right below the one where you enter your wage income.
If your tax bracket is 10%, you could owe 10% of of the additional income in tax.
The current column is the amount of interest earned this month; the YTD colum is the amount of interest earned since the beginning of the year. The amount for YTD on the December statement is the one that will be reported to you on the 1099-INT and is the amount you put on your tax return.